IMPORTANT: the historic distinction between MARS Light and the future MARS Full has been dropped. Now all versions are simply called "mars". Old tagnames light* will remain valid, but newer names will follow the convention s/light/mars/g (this means that the old version number counting will be continued, only the "light" is substituted). Meaning of stable tagnames -------------------------- Example: mars0.1stable01: 0 = version of on-disk data structures (only incremented when downgrades are impossible) (not incremented on backwards-compatible upgrades) 1 = version of feature set stable = feature set is frozen during this series 01 = bugfix revision Example: mars0.2beta2.3: The general idea is as before. "beta" means that new features are roughly tested in the lab, but not in production, so there may be some bugs. New features may be added during the beta phase. Example: mars0.3alpha*: Never use this for production. Only for historic code inspection. Release Conventions / Branches / Tagnames ----------------------------------------- FLOW OF BUGFIXES: 0.1 -> 0.1a -> 0.1b -> 0.2 -> ... mars0.1 series (stable, will go EOL soon): - Will run in parallel to branch 0.1a for a few months, and then go EOL. - Unstable tagnames: light0.1beta%d.%d (obsolete) - Stable branch: mars0.1.y - Stable tagnames: mars0.1stable%02d mars0.1a series (stable): New master branch. Now stable. This branch is operational for several years on several thousands of servers, and several petabytes of data. - Unstable tagnames: light0.1abeta%d (obsolete) - Stable branch: mars0.1a.y - Stable tagnames: mars0.1astable%02d mars0.1b series (currently alpha): This is an _imtermediate_ series between 0.1 and 0.2. The goal is to improve _scalability_ to thousands of hosts in one cluster, as well as thousands of resources. Likely, this intermdiate branch will be merged into 0.2 and then continue development there. When this point will arrive is uncertain at the moment. Likely, the stabilization of the new scalability features will occur together with the 0.2 series. Reason for this: the rollout strategy at 1&1 to thousands of machines wants to do small incremental steps. The risk of directly going to 0.2 in _masses_ is minimized by first rolling out the really necessary changes, and to postpone those developments which are currently not yet really needed in mass deployment. mars0.2 series (currently in beta stage): Mostly for internal needs of 1&1 (but not limited to that). - Getting rid of the kernel prepatch! MARS may be built as an external kernel module for any supported kernel version. First prototype is only tested for unaltered 3.2.x vanilla kernel, but compatibility to further vanilla kernel versions (maybe even Redhat-specific ones) will follow during the course of the MARS mars0.2 stable series. The problem is not compatibility as such, but _testing_ that it really works. These tests need a lot of time. => further arguments for getting to kernel upstream ASAP. - Improved network throughput by parallel TCP connections (in particular under packet loss). Also called "socket bundling". First benchmarks show an impressive speedup over highly congested long-distance lines. - Future-proof updates in the network protocol: Mixed operation of 32/64bit and/or {big,low}endian - Support for multi-homed network interfaces. - Transparent data compression over low bandwidth lines. Consumes a lot of CPU, therefore only recommended for low write loads or for desperate network situations. - Remote device: bypassing iSCSI. In essence, /dev/mars/mydata can appear at any other cluster member which doesn't necessarily need any local disks. - Various smaller features and improvements. - Unstable tagnames: mars0.2beta%d.%d (current) - Stable branch: mars0.2.y (already in use for beta) - Stable tagnames: mars0.2stable%02d (planned) mars0.3 series (planned): (some might possibly go to 1.0 series instead) - Improve replication latency. - New pseudo-synchronous replication modes. For the internal needs of database folks at 1&1. - (Maybe) old test suite could be retired, a new one is at github.com/schoebel/test-suite - Unstable tagnames: mars0.3beta%d.%d (planned) - Stable branch: mars0.3.y (planned) - Stable tagnames: mars0.3stable%02d (planned) mars1.0 series (planned): - Replace symlink tree by transactional status files (future-proof) This is required for upstream merging to the kernel. It has further advantages, such as better scalability. - Trying to additionally address public needs. - Potentially for Linux kernel upstream, - Unstable tagnames: mars1.0beta%d.%d (planned) - Stable branch: mars1.0.y (planned) - Stable tagnames: mars1.0stable%02d (planned) WIP-* branches are for development and may be rebased onto anything at any time without notice. They will disappear eventually. *stable* branches mean that only bug fixes and documentation updates / clarifications will be applied. Updates to the test suite / new test cases potentially disguising bugs, and other minor additions of debugging code / paranoia code which may lead to discovery of bugs are also possible. Error messages / warnings and their error class may also be changed. NO NEW FEATURES, not even minor ones, except when absolutely necessary for a bugfix, or for an important usability improvement (such as clearer display of errors, hints for resolving them, etc). ----------------------------------- Changelog for series 0.2: (you need to checkout branch mars0.2.y to see any details) ----------------------------------- Changelog for series 0.1b: (you need to checkout branch mars0.1b.y to see any details) ----------------------------------- Changelog for series 0.1a: (you need to checkout branch mars0.1a.y to see any details) Designated master branch in future. Recommended for Football. Will get updates on the Football sub-project. Based on 0.1balpha4. Merge 0.1stable. Receive mainly fixes. ----------------------------------- Changelog for series 0.1: Attention! This branch will go EOL around February 2019. Branch mars0.1a.y is now the new master branch, and all commits from the 0.1 series will be fully merged. Upgrade is easy: just rollout the new marsadm version, install the new kernel modules, and load them where possible. Mixed operation of different versions is no problem, but is of course not the desired state, so keep this period as short as possible. Rollback is also easy. Motivation: branch 0.1a is productive for several years at 1&1. Experiences: now runs provably better than 0.1.y with better performance, smoother, etc. And even more stable, although the 0.1a releases were called "beta" up to now. mars0.1stable68 * Minor fix: detach could hang under very weird circumstances. * Minor fix: in extremly rare cases and under further conditions, detach could hang due to a race. Workaround was possible by re-attaching. * Minor improvement: /dev/mars/mydata now disappears only after writeback has finished. Although the old behaviour was correct, certain userspace tool could have erronously concluded that the primary has finished working. The new bevaiour is hopefully more like to user expectance. * Minor improvement: propagate physical and logical sector sizes from the underlying disk to /dev/mars/mydata. This can affects mkfs and other tools for making better decisions about their internal parameters. * Minor safeguard: disallow manual --ignore-sync override when the target primary is inconsistent, only relevant for (non-existent) sysadmins who absolutely don't know what they are doing when they are combining this with --force. Systemadmins who really know what they are doing can use fake-sync in front of it, and then they are explicitly stating once again that they really want to force a defective system, and that they really know the fact that it is defective. * Minor improvement: propagate logical and physical sector sizes from the underlying disk to the virtual mars device. * Minor improvement: additional warning when network connections are interrupted (asymmetrically), such as by mis-configuration of network interfaces / routing / firewall rules / etc. mars0.1stable67 * Minor fix: don't unnecessarily alert sysadmins when no systemd unit files are installed. * Minor doc update: new slides from LCA2019, updated old slides from FrOSCon2018. * Minor doc update: describe some more use cases, add some advice for managers. mars0.1stable66 * Critical fix, only relevant for kernels 4.3 to 4.4: Due to a forgotten adaptation to newer kernels, some userspace tools like xfs_repair could read/write wrong data upon _large_ IO requests, and/or kernel memory corruption could occur. Kernel-level filesystems are typically _not_ affected because they typically use 4k pages at maximum. If you are operating such a kernel, please upgrade to minimize any risks. You probably want userspace tools like xfs_repair to not crash your kernel ;) The problem was reproducibly detected at lab regression testing, _before_ updating a big installation from kernel 3.16 to 4.4. It did not show up with the old kernel. Notice: kernels >4.6 are not yet supported at the moment, but work on them is likely being continued during the next months. Stay tuned. * Minor doc updates. mars0.1stable65 * Major fix, only observed during KASAN debugging: Use-after-free which appears to splat only at Football during final deletion of resources. Never observed at production. Update if you are very cautious. * A few minor fixes, not relevant for production. * Minor doc improvements. mars0.1stable64 * Major regression: split-brain detection did not display correctly. * Minor fix: rare race conditon on O_NONBLOCK networking. Only observed during testing with kernel 4.9 (sorry, _all_ the adaptations are not yet ready for release, but it is making progress now). I am not sure whether this bug could also trigger with kernel 4.4 or earlier, therefore I am releasing the fix beforehand. * Minor doc architectural explanations. mars0.1stable63 * Minor fix: when compiling for some newer kernels (only there), schedule() could be called during wait for some condition, worsening performance unnecessarily. * Minor improvement: starting join-resource in batches was slow because each was waiting for cluster communication. Use a manual "marsadm wait-cluster" before starting batches of join-resource operations. * Doc: some clarifications on BigCluster scalability behaviour. mars0.1stable62 * Minor fix: race between join-resource and log-rotate. * Minor fix: report split brain logfile amount only when actually detectable. * Minor improvement: shift annoying error message over to Orphan state detection. * Football: update to Football-2.0-RC12 * doc: some updates. mars0.1stable61 * Minor fix: in very rare cases where some symlinks are missing, don't abort in try_to_avoid_splitbrain(). * Minor improvement: better human-readable numbers. * Minor doc: more on asynchronous background operations. mars0.1stable60 * Major improvement: new option --ignore-sync allows primary Handover without --force even when some sync is running somewhere. Any running syncs will restart from scratch (which might take some time, depending on LV size and many more factors like the network). * Minor fix: split-cluster did not work correctly when no resources were existing anymore, at all. * Doc: major update. More explanation on CAP theorem, and on differences / commonalities with DRBD. mars0.1stable59 * Major fix: "marsadm up" did not work when sync could not be started. Now does "best effort". * Minor fix: marsadm system interface was active when not activated. * Minor usability improvement: new repliaction state "Orphaned" indicates that logfiles are missing, and thus replication is stuck. mars0.1stable58 * Major fix for Football / split-cluster: for safety, cron deletes some blocking left-overs. * Major fix at _asymmetric_ split-cluster: ignore hindering abort condition. * Minor fix: not all internal systemd links were removed upon marsadm set-systemd-unit mydata "". * Doc: Football. * Doc: architectural treatment of centralized storage. mars0.1stable57 * Minor fix: silly deadlock upon scarce race at logging. Without debug logging, probability should be extremely low (only observed at rmmod). * Added initial version of systemd templates (for future backward compatibility with branch 0.1a). * Doc: systemd templates. mars0.1stable56 * Minor fix: split-cluster could unnecessarily abort in some cases. * Added initial version of submodule "football". More updates will follow. mars0.1stable55 * Major fix: unnecessary / false positive split brain could occur after the primary logfile was truncated, e.g. at crashes or disk damages. Systematic triggering in masses was possible by keeping /dev/mars/mydata mounted while _forcing_ a reboot _during_ (!) its umount (e.g. by patching the "reboot" command and/or patching systemd dependencies or similar to provoke this regularly). mars0.1stable54 * Major fix, only relevant for massive execution of leave-resource, e.g. when playing Football (Tetris) games: When non-versioned symlinks were eventually deleted, later re-creation did not always succeed. Fixed by an new generic timestamp ordering approach. * Stability client-side fixes (could lead to stacktraces), backported from branch 0.1a (were forgotten long ago). * Major doc update: new section on reliability of storage architectures. This explains why many BigCluster systems don't work as expected. Backed up by graphs and by mathematical formulas. A must-read for anyone working in the storage area! mars0.1stable53 * Major fix: rare corner case of split brain was not displayed correctly. * Major usablilty: show amount of data during split brain. This hints the sysadmins about the size of future data loss at later split brain resolution. * Minor workaround: crashed /mars filesystems may contain completely damaged symlinks with timestamps in the far distant future, e.g. year >3000 etc. Safeguard unusual Lamport time slips by ignoring implausible values. * Major improvement: internal locking overhead reduced. * Minor improvment: reduce message trigger overhead. * Several minor improvements. * Doc updates. mars0.1stable52 * Major contrib: new example scripts for MARS background data migration during production. 1&1-specific code in a separate plugin. You can write your own plugins for adaptation to your needs. * Minor fix: limit the size of the writeback buffer by the rest space in /mars. This is only relevant when /mars is dimensioned smaller than RAM (which should never be the case in production systems, but might happen accidentally or for testing). Analogously, limit the maximum logfile size. * Minor fix: prevent creation of many tiny logfiles over time when secondaries are not catching up. The default threshold is a minimum of 5 GB size when more than 10 logfiles are already present. * Minor fix: cleanup old internal .tmp-* symlinks which might remain as leftovers when marsadm is dying at the wrong moment. * Minor improvement: don't run O(n) mapfree under spinlock. More speed improvements under preparation; will result in O(k). * Some more minor improvements. mars0.1stable51 * Minor fix: don't abort log-delete-all too early when there are holes in the deletion sequence numbers. * Backport of marsadm cron from branch 0.1a, in order to systematically support mixed operation of different MARS versions in bigger installations (avoid confusion at junior sysadmins and at monitoring staff). * Rectified the semantics of log-delete, which now does the same as log-delete-all. Single deletion is only needed for testing, and has been renamed to log-delete-one. Leaving the old semantics would have been an operational risk when junior sysadmins or 24/7 surveillance people are not carefully looking at the details of semantics. Now everything is hopefully as everybody not familiar with MARS would naively assume. * Doc update. mars0.1stable50 * Major usability improvement (backport from 0.1a): marsadm shows number of replicas of each resource, out of total number of cluster members. Example: [2/4] * Minor fix: automatically cleanup internal backups produced by the new merge-cluster / split-cluster after 1 week. * Minor fix: also cleanup some new symlink types replicated through the network when running asymmetric clusters with mixed branches 0.1 and 0.1a. * Minor annoyance: silence split-cluster error message when no resources are present. mars0.1stable49 * Backports of new marsadm commands merge-cluster and split-cluster. The new functionality is needed for background migration of resources. Please be aware that this branch has not been constructed for scalability in the dimension of #nodes, so don't merge too many nodes and use split-cluster after each background migration. Better scalability is / will be addressed at the 0.1a and 0.1b branches. However, currently they are not yet stable. No changes at the kernel module (besides some bug fixes); this is solely done at userspace level. The new userspace-level commands should have almost no intersection with (and therefore no impact onto) other parts of this well-proven stable branch. * Backports of new wait-cluster implementation. This avoids irritating messages after split-cluster. mars0.1stable48 * Critical fix: DDOS-like attacks at the MARS ports (or similar caused by bugs / misbehaviour) are prevented by configurable limits /proc/sys/mars/handler_dent_limit and /proc/sys/mars/handler_limit . * Critical safeguard: when the network is interruted for a long time while the log-rotate frequency is very high and a lot of resources (exceeding the official limits as documented) had been used, masses of deletion links may accumulate in /mars/todo/. First, already existing deletions to the same targets are reused now. Second, a maximum limit (of currently 512 entries) is enforced, and a warning is spit when too many deletions are accumulated over time. * Minor fix: earlier detection of socket hangups. mars0.1stable47 * Critical fix: leave-cluster could lead to deadlocks, also on remote nodes. * Contrib: mass automation script (unmaintained). mars0.1stable46 * Major fix: bugfix from 0.1stable44 (state "Detached" was reported too early) was incorrect, now fixed. * Minor fix: display of host lists in special case of create-resource was misleading. mars0.1stable45 * Major fix: on secondaries, orphane files and symlinks were sometimes created in /mars and could accumulate over a long time. After several months or years of operation, the /mars directory could appear being full via "df /mars", but "du -s /mars" was not reporting the hidden space allocation. Also, upon remount or reboot the cleanup of orphane files could take a rather long time. Workaround was possible by "rmmod mars; umount /mars; mount /mars; modprobe mars". Fixed by regularly pruning the dentry cache of the /mars filesystem. mars0.1stable44 -------- * Major fix: state "Detached" was reported too early, before the underlying disk was really closed. * Doc: new updated slides from FrOSCon 2017. New architectural comparison with Big Storage Clusters in terms of scalability, reliability and costs. mars0.1stable43 -------- * Major fix, only relevant for k >= 3 replicas: Logfile fetch did not switch over to another alive peer upon _speicfic_ network problems with the _current_ peer. As a consequence, an unaffected replica could hang. Workarould was possible by pause-fetch / resume-fetch or by fixing the network :) mars0.1stable42 -------- * Minor fix: ssh IPs and port numbers are automatically probed on join-cluster. * Minor compatibility to branch mars.1b.y: join-resource does additional rsync for safety. * Minor fix: rate display was not going down to 0 on switchoff or long pauses. * Minor improvement: show peers in internal debugging info. mars0.1stable41 -------- * Minor fix: a scarce race could lead to an unnecessary split brain when umounting _after_ role transition from primary to secondary. mars0.1stable40 -------- * Potentially critical fix: on very fast machines, and with extremely low probability, a race in AIO could lead to a kernel page fault. For maximum safety, update to this version is recommended. mars0.1stable39 -------- * Minor fix: hangs of logfile updates. Found by stress-testing on fast hardware over 10GBit network links. Might explain some extremely rare (1 per several millions of operations hours) production hangs on secondaries. Workaround possible by "pause-fetch; resume-fetch". * Minor fixes of rare kthread retarding under very high load. * Minor improvement: add version number to "marsadm version" which can be used for future compatibilty checking with respect to new features. mars0.1stable38 -------- * Compile without pre-patch on some kernel versions! Whether the pre-patch is applied will be detected automatically. However, there is some (hopefully minor) performance penalty when the pre-patch is missing. This will be addressed in a future release (but might go to branch 0.1b instead, not yet decided). Tested with vanilla kernels 3.10.105, 3.14.79, 3.16.43, 4.1.39, 4.4.67. Vanilla kernels 4.8.x and later are _not_ yet working (independently from pre-patches). This will be addressed in a future release. * No functional changes otherwise. Rollback to prior versions should be easy. Please report any issues. * Updated docs describing build methods. mars0.1stable37 -------- * Minor fix: secondary logfile replication could hang in the extremely unusual case that the expected primary logfile size gets shortened after a crash followed by reboot. Workaround was possible via "pause-fetch; resume-fetch". mars0.1stable36 -------- * Doc: new slides from GUUG2017, both in English and in German. Some very important hints for cost savings. May easily save you a few millions when operating some petabytes of data. * Doc: new chapter on cost savings in mars-manual.pdf. Some parts of German oral explanations from the GUUG conference translated to English for my English-speaking audience. More to come later (hopefully; I need to get the time). mars0.1stable35 -------- * Minor fix: when syncing a big resource (e.g. 40TiB) over an 1GBit uplink, the sync may take longer than 1 day. This increases the probability for triggering an unintended restart of that sync from scratch. Among further obscure preconditions, more than 5 logfiles must exist such that the wrong assumption of an emergency mode can happen at the secondary. In order to trigger the bug more likely, it is therefore helpful to misconfigure /etc/cron.d/mars by log-rotate'ing every 10 minutes, but doing log-delete-all only once an hour (which contradicts my upstream documentation and unnecessarily wastes valuable storage space in /mars). Fixed by correction of a typo-like error. mars0.1stable34 -------- * Minor fix: in some rare cases, when lots of gigabytes had to be replayed in one big slurp, the replay position wasn't updated during a longer time. Some admins were complaining that it appeared "stuck" although it worked in reality. Improved by increasing the update frequency of the replay link. * Minor fix: after network errors, sometimes the sync restarted from scratch, unnecessarily. * Minor fix: under rare conditions, rmmod could hang forever. A known reason has been fixed. Other theoretical reasons hopefully improved by some further safeguards. mars0.1stable33 -------- * Minor regression from stable29: After a primary crash, without switchover, and when the primary recovery phase involves a logrotate to an empty new logfile which had been in the meantime shortly before the crash but has not yet been used before the crash (race condition), a kernel NULL pointer deref may stop the main thread. Workaround: either remove the empty logfile by hand, or just do a failover to the other side. mars0.1stable32 -------- * Critical regression between stable30 and stable31 (can be avoided by simply using stable30 for affected kernels): on _old_ kernels (before 4.3.x) the removal of merge_bvec_fn() (see upstream commit 8ae126660fddbeebb9251a174e6fa45b6ad8f932) can lead to fatal crashes at the primary side. Fixed by using (hopefully) proper #ifdef's according to the kernel version. Notice: between stable30 and stable31 no true MARS fixes were made (since no bugs were found). This strategy is likely to continue for a while, for newer adaptations to even newer kernels. In case of problems, go back. And, please, report it to me :) mars0.1stable31 -------- * New _minimum_ pre-patches for vanilla LTS kernels 3.2.x to 4.7.x. For security reasons, please prefer them over the old _generic_ pre-patch versions which expose many unnecessary EXPORT_SYMBOL to potential attackers. * Adaptions to vanilla kernels up to 4.7.x. Note: 4.8rc-* does not yet work. * Regression testing with many kernel versions: looks fine. mars0.1stable30 -------- * Minor fix: in very rare cases of a primary crash, a missing versionlink could lead to a hang. * Minor fix: improved error reporting of replay code. * Minor fix: improved switchback to former primary side. * Minor fix: systematically add some missing macros. * Minor improvements: add some example systemd unit and other contrib stuff like a cronjob example. * Doc: minor additions and improvements. mars0.1stable29 -------- * Minor fix: on very fast hardware and networks, sync could take a while for terminating. * Minor fix: external module build. * Major usability improvement: new expert commands marsadm lowlevel-ls-host-ips, lowlevel-set-host-ip, lowlevel-delete-host. Necessary for moves between networks, dedicated replication IPs, etc. * Minor doc update. mars0.1stable28 -------- * Doc: describe new naming conventions. MARS Light is now simply called MARS. No distinction between "Light" and the future "Full" anymore. Please note that the git branches light0.1.y and light0.2.y have been renamed to mars0.1.y and mars0.2.y respectively. * Minor sourcecode cleanup: s/light//g or s/light/main/g where appropriate. No other changes in the sourcecode, deliberately. In case anyone encounters any build problems compiling MARS, this release is separated just for the sake of build testing, or Debian packaging testing, etc. * Doc: minor clarifications. mars0.1stable27 light0.1stable27 -------- * Critical fix: typo in sync progress comparison code could lead to data version mismatches during sync when alternating with replay. Only observed at a certain new hardware class, and only while testing with an extremely high load (9 loaded resources in parallel to 9 concurrent syncs). As a workaround, echo 0 > /proc/sys/mars/sync_flip_interval_sec can be used. Nevertheless, update is highly recommended! * Major fix: slow memory leak (regression from light0.1stable26). Only when starting the transaction logger (i.e. primary is typically not affected). But don't let run it for a longer time. Monitoring is possible via /proc/slabinfo (size-64 or siblings). * Minor fix: join-cluster did not check for duplicate IP addresses. * Minor fixes: some unnecessary annoying error messages. * Docu: new slides from GUUG 2016 in Köln. light0.1stable26 -------- * Minor fixes: some primitive macros were reporting misleading or even wrong values at split brain, or during/after emergency mode. Some high-level macros as well as try_to_avoid_split_brain should work better / more reliable now. * Minor fix: potential deadlock after crash reboot, or after defective /mars filesystem. Never observed in practice. * Minor safeguard: unnecessary split brain could emerge at secondaries under extremely rare and strange conditions. Unsure whether it ever occurred in practice. * Minor usability improvement: show incorrect permissions on /mars. Some other sysadmin tools like Puppet seem to have their own default notion of "secure permissions" ;) * Minor doc reorg, better chapter structure. light0.1stable25 -------- * Major fix: in rare cases "marsadm primary" (without --force) could go into an endless loop, even if --timeout= was specified. * Minor fix: in rare cases of hanging or defective IO, crashes of the primary could replicate versionlinks to the secondary, but after reboot they were missing at the primary because of of hanging IO or other IO / RAID controller problems. Now using sync_filesystem() for either ensuring actuality, or for letting the mars_light main control thread hang (which will hopefully be noticed soon by monitoring). * Minor fix: join-cluster uses rsync, which could abort due to vanished filesystem objects while the primary is actively running. Now it should tolerate such "errors". * Minor fixes / additions at primitive macros. * Tiny doc update. light0.1stable24 -------- * Skip this release due to a regression. light0.1stable23 -------- * Minor fix: the new replay-code error message was forgotten to reset at secondaries. Now the annoying old error message disappears after the next successful logrotate. * Minor fixes of internal marsadm code (not in use until now). * Minor doc update. light0.1stable22 -------- * Critical fix for non-storage servers: the /mars directory was readable by ordinary non-root users, opening a potential security hole. Originally MARS was designed for standalone storage servers solely, but now it is increasingly deployed to machines where ordinary users can log in. Update recommended, but only urgent for potentially affected installations. * Minor fix: when a logfile was damaged (observed at defective hardware), this was often (but not always) detected by the md5 data checksums in the transaction logfiles. So far so good. The replay / recovery process stopped for a very good reason. But it was not easily possible to _force_ any of the resource members into primary role when the defect was already present at the _primary_ (which happend once during 7 millions of operating hours, and at a primary site which proved defective afterwards), and the defect had been replicated to all secondaries. As a workaround, the resource could be destroyed via leave-resource everywhere, and re-surrected from scratch. Clumsy. Now an md5 checksum error in the middle of a logfile is treated similarly to an EOF. "primary --force" will succeed now, without applying the defective data (as before). Split brain will result for sure in such a case. * Minor improvement: md5 logfile checksum errors are now displayed directly in the diskstate macro (and therefore also at plain "view"). * Minor improvement: when "marsadm view all" told you "InConsistent" as the disk state, this was _formally correct_ because it related to the state of the _disk_, not to the state of the replication. The former message could appear regularly during ordinary out-of-order writeback at the primary side, without violating the consistency of /dev/mars/mydata. However, many people were confused and alarmed by the irritating message. Now a better wording is used: "WriteBack" and "Recovery" describes more intuitively what is really happening :) * Minor doc improvements. light0.1stable21 -------- * Hint: now MARS has been rolled out to more than 1600 servers, including some MySQL database servers, and has collected more than 6 millions of operation hours. * Minor fixes, none of them observed in practice, only found by testing while working on new features: - potential read page fault - potential deadlock - incorrect remote symlink update under untypical circumstances light0.1stable20 -------- * Hint: MARS is now running on more than 850 storage servers, and has collected more than 4.5 millions of operation hours. There were no new incidents with customer impact since the last major bugfix (more than 3 millions of operation hours since then). It is difficult to deduce a reliability from that, but it appears that at least 99.999%, if not 99.9999% are now real for the MARS component as a standalone component (not to be confused with overall system reliability). Our storage hardware is clearly much less reliable. MARS does compensate these defects all the time. * Minor fix: memory leak in networking code, does not occur at light0.1 operations (but maybe future versions of MARS). * Doc: add presentation slides from Froscon2015. light0.1stable19 -------- * Minor safeguard: warn when somebody tries leave-resource --host= for a damaged host, and later the dead host resurrects in an unreasonable way. * Doc update: describe use cases for DRBD vs MARS more clearly. * Minor spelling fixes. light0.1stable18 -------- * Minor safeguard: prevent join-resource when previous log-purge-all has been forgotten. Prevent create-resource also when previous delete-resource has been forgotten. Anyway, this happens only in very exotic repair scenarios after very heavy failures. * Doc updates: simplify descriptions of split-brain resolution and emergency mode resolution. Nowadays 'invalidate' will do everything in all tested cases; the more complex alternative methods have been moved to the appendix. light0.1stable17 -------- * Minor fix: stacktrace / oops in aio callback path due to a subtle race, observed once during 2.5 millions of operation hours. In the observed case, the secondary was hanging, without customer impact. However, the error class could potentially occur also at the primary side. Probably the bug was triggered by a hardware problem from the RAID controller. light0.1stable16 -------- * Minor fix: sync could take a long time to complete under high application load, similarly to a live-lock. * Some smaller minor fixes for annoying messages. * Contrib: added configurable Nagios check. * Contrib: added some example scripts which could be used by clustermanagers etc. * Doc: important new section on pitfalls when using existing clustermanagers UNMODIFIED for long distance replication. PLEASE READ! light0.1stable15 -------- * NOTICE: MARS succeeded baptism on fire at 04/22/2015 when a whole co-location had a partial power blackout, followed by breakdown of air conditioning, followed by mass hardware defects due to overheating. MARS showed exactly 0 errors when (emergency) switching to another datacenter was started in masses. * Major fix of race in transaction logger: the primary could hang when using very fast hardware, typically after ~24000 operation hours. The problem was noticed 6 times during a grand total of more than 1,000,000 operation hours on a mixed hardware park, showing up only on specific hardware classes. Together with 3 other incidents during early beta phase which also had customer impact, this means that we have reached a reliability of about ===> 99.999% After this fix, the reliability should grow even higher. A workaround for this bug exists: # echo 2 > /proc/sys/mars/logger_completion_semantics Update is only mandatory when you cannot use the workaround. * Minor improvement in marsadm: re-allow --force combined with "all". This is highly appreciated for speeding up operations / handling during emergency datacenter switchover. * Various smaller improvements. * Contrib (unsupported): example rollout script for mass rollout. light0.1stable14 -------- * Minor safeguard: modprobe mars will refuse to start when the cluster UUID is missing. * Minor fix: external race in marsadm resize, only relevant for scripting. * Minor fix: potential race on plugged IO requests. * Clarify output of marsadm view. Many systematical improvements and hints. * Add some unevitable macros for scripting / automation. * Various tiny improvements. light0.1stable13 -------- * Critical safeguard for accidental join-cluster with wrong argument: make UUID mandatory, disallow completely unrelated hosts to communicate symlink tree updates when their UUIDs mismatch. * Minor fix: leave-resource --host=other did not work when disks were named differently throughout the cluster. * Minor fix: detach --host=other --force (which is needed as a precondition) did not work. * Various minor fixes and clarifications. "marsadm view all" now reports the communication status in the cluster. light0.1stable12 -------- * Critical (but usually not extremely relevant) fix: When emergency mode occurs just during a sync, the target could remain inconsistent without notice. Now noticed. You always could/should manually invalidate whenever an emergency mode appeared. Now this is automatically fixed by restarting any sync from scratch (if one was actually running before; otherwise consistency was never violated). * Major documentation update / corrections. * Major (but less relevant) fix: leave-cluster did not really work. * Minor fix (regression): rmmod could hang when sync was running. * Various minor fixes and clarifications. light0.1stable11 -------- * Major documentation update. mars-manual.pdf increased from 66 to 80 pages. Please read! You probably should know this. * Minor fixes: better cleanup on invalidate / leave-resource. * Minor clarifications: more precise EIO error codes, more verbose error reporting via "marsadm cat". light0.1stable10 -------- * Major fixes of internal network protocol errors, leading to internal shutdown of sockets, which were transparently re-opened. It could affect network performance. Not sure whether stability was also affected (probably under extremely high load); for better safety you should upgrade. * Major fix from Manuel Lausch: regex parsing sometimes went completely wrong when hostnames followed a similar name scheme than internal symlinks. * Major, only relevant for k>2 replicas: fix wrong internal sharing of data structures resulting from parallel data connections. * Minor fix: race in fake-sync. * Minor fix: race in invalidate. * Minor, only for k>2 replicas: fix direct primary handover when some non-involved hosts are currently unreachable. * Minor: improve becoming primary during split brain. * Minor: improve becoming primary when emergency mode starts. * Minor: silence some annoying stderr messages. * Several internal minor fixes and clarifications. light0.1stable09 -------- * Major fix of scarce race (potentially critical): the bio response thread could terminate too early, leading to a premature dealloc of kernel memory. This has only been observed on slow virtual machines with slow virtual devices, and very high load on k=4 replicas. This could potentially affect the stability of the system. Although not observed at production machines at 1&1, I recommend updating production machines to this release ASAP. * Major usability fix: incorrect commandline options of marsadm were just ignored if they appeared after the resource argument. Misspellings could cause undesired effects. For instance, "marsadm delete-resource vital --force --MISSPELLhost=banana" was accidentally destroying the primary during operation (which is _possible_ when using --force, and this was even a _required_ sort of "STONITH"-like feature -- however from a human point of view it was intended to destroy _another_ host, so this was an unexpected behaviour from a sysadmin point of view). * Major workaround: the concept "actual primary" is wrong, because during split brain there may exist several primaries. Do not use the macro view-actual-primary any longer. It is deprecated now. Use view-is-primary instead, on each host you are interested in. * Minor fix: "marsadm invalidate" did not work in some weired split brain situations / was not equivalent to "marsadm leave-resource $res; marsadm join-resource $res". The latter was the old workaround to fix the situation. Now it shouldn't be necessary anymore. * Minor fix: pause-fetch could take very long to terminate. * Minor fix: marsadm wait-cluster did not wait for all hosts particiapting in the resource, but only for one of them. This is only relevant for k>2 replicas. * Minor fix: the rates displayed by "marsadm view" did not drop down to 0 when no progress was made. * Minor fix: logging to syslog was incomplete. * Minor usability fix: decrease boring speakyness of "log-rotate" and "log-delete" for cron jobs. * Minor fixes: several internal awkwardnesses, potentially affecting performance and/or stability in weired situations. light0.1stable08 -------- * Minor fix: after emergency mode, a versionlink was forgotten to create. This could lead to unnecessary reports of split brain and/or need for additional re-invalidate. * Minor fix: the predicate 'view-is-consistent' reported 'false' in some situations on secondaries when all was ok. * Minor fix: it was impossible to determine the 'is-consistent' from 'marsadm view' (without -1and1 suffix). Added a new [Cc-] flag. This is absolutely needed to determine whether the underlying disks must have the same checksum (provided that both disks are detached and the network works and fetch+replay had completed before the detach). * Updated docs to reflect this. * Minor fix: 'invalidate' did not work when the resource was not completely detached. Now it implicitly does a detach before starting invalidation. * Minor fix: wait-umount was waiting for umount of _all_ primaries during split brain. Now it waits only for umount of the local node. Notice that having multiple primaries in parallel is an erroneous state anyway. * Minor fix: leave-cluster did not work without --force. light0.1stable07 -------- * Minor fix: re-creation of a completely destroyed resource did not always work correctly light0.1stable06 -------- * Major fix: becoming primary was hanging in scarce situations. * Minor fix: some split brains were not always detected correctly. * Minor fix for Redhat openvz kernel builds. * Several fixes for 1&1 internal Debian builds. light0.1stable05 -------- * Major fix: incomplete calls to vfs_readdir() which could lead to incomplete symlink updates / replication hangs. * Minor fix: scarce race on replay EOF. * Separated kernel from userspace build environment. * Removed some potentially dangerous Kconfig options if they would be set to wrong values (robustness against accidentally producing bad kernel modules). * Dito: some additional checks against bad main Kconfig options (mainly for out-of-tree builds). * Separated contrib code from maintained code. * Added some pre-patches for newer kernels (WIP - not yet fully tested at all combinations) * Minor doc addition: LinuxTag 2014 presentation. light0.1stable04 -------- * Quiet annoying error message. * Minor readability improvements. * Minor doc updates. light0.1stable03 -------- * Major: fix internal aio race (could lead to memory corruption). * Fix refcounting in trans_logger. * Some minor fixes in module code. * Fix 1&1-internal out-of-tree builds. * Various minor fixes. * Update monitoring tools / docs (German, contributed by Jörg Mann). light0.1stable02 -------- * Fix sorting of internal data structure. * Fix IO error propagation at replay. light0.1stable01 -------- * Fix parallelism of logfile propagation: sometimes a secondary could get a more recent version than the primary had on stable storage after its crash, eventually leading to an (annoying) split brain. Some people might take this as a feature instead of a bug, but now the logfile transfer starts only after the primary _knows_ that the data is successfully committed to stable storage. * Fix memory leaks in error path. * Fix error propagation between client and server. * Make string allocation fully dynamic (remove limitation). * Fix some annoying messages. * Fix usage output of marsadm. * Userspace: contributed bugfix for Debian udev rules by Jörg Mann. * Improved debugging (only for testing). light0.1beta0.18 (feature release) -------- * New commands marsadm view-$macroname * New customizable macro processor * New err/warn/inf reporting via symlinks * Per-resource emergency mode * Allow limiting the sync parallelism * New flood-protected syslogging * Some smaller improvements * Update docs * Update test suite light0.1beta0.17 -------- * Major bugfix: race in logfile switchover could sometimes lead to the wrong logfile (extremely rare to hit, but potentially harmful). * Disallow primary switching when some secondaries are syncing. * Fix logfile fetch from multiple peers. * Fix computation of transitive closure (affected log-purge-all, split brain detection, and many others). * Fix incorrect emergency mode detection. * Primaries no longer fetch logfiles (unnecessarily, only makes a difference at concurrent split brain operations). * Detached resources no longer fetch logfiles (unexpectedly). * Myriads of smaller fixes. light0.1beta0.16 -------- * Critical bugfix: "marsadm primary --force" was assumed to be given by sysadmins only in case of emergency, when the network is down. When given in non-emergency cases where the old primary continues to run (/dev/mars/* being actively used and written), the old primary could suddendly do a "logrotate" to the new split-brain logfile produced by the new (second) primary. Now two primaries should be able to run concurrently in split-brain mode without mutually trashing their logfiles. * primary --force now only works in disconnected mode, in order to hinder unintended forceful creation of split brain during normal operation. * Stop fetching of logfiles behind split brain points (save space at the target hosts - usually the data will be discarded later). * Fixed split brain detection in userspace. * leave-resource now waits for local actions to take place (remote actions stay asynchronously). * invalidate / join-resource now work only if a designated primary exists (otherwise they would not know uniquely from whom to start initial sync). * Update docs, clarify scenarios intended <-> emergengy switching. * Fixed mutual overwrite of deletion symlinks in case of racing log-deletes spawned in parallel by cron jobs (resilience). * Fixed races between deletion and re-erection (e.g. fresh join-resource after leave-resource during network partitions). * Fixed duration of network timeouts in case the network is down (replaced non-working TCP_KEEPALIVE by explicit timeouts). * New option --dry-run which does not really create symlinks. * New command "delete-resource" (VERY DANGEROUS) for forcefully destroying a resource, even when it is in use. Intended only for _emergency_ cases when sysadmins are desperate. Use only by hand, first run with --dry-run in order to check what will happen! * New command "log-purge-all" (potentially DANGEROUS) for resolving split brain in desperate situations (cleanup of leftovers). Only use by hand, first run with --dry-run! * Lots of smaller imprevements / usability / readability etc. * Update test suite. light0.1beta0.15 -------- * Introduce write throttling of bulk writers. * Update test suite. light0.1beta0.14 -------- * Fix logfile transfer in case of "holes" created by emergency mode. * Fix "marsadm invalidate" after emergency mode had been entered. * Fix "marsadm resize" capacity propagation from underlying LVM. * Update test suite. light0.1beta0.13 -------- * Fix shutdown during operation (flying requests). * Fix unnecessary Lamport clock propagation storms. * Improve unnecessary page cache utilisation (mapfree). * Update test suite. light0.1beta0.12 and earlier -------- There was no dedicated ChangeLog. For details, look at the commit history. Release Policy / Software Lifecycle ----------------------------------- New source releases are simply announced by appearance of git tags.