diff --git a/NEWS b/NEWS index ba9077f9..6defe4a3 100644 --- a/NEWS +++ b/NEWS @@ -1 +1 @@ -see https://github.com/schoebel/mars +See http://schoebel.github.io/mars/ diff --git a/README b/README index 59180793..6defe4a3 100644 --- a/README +++ b/README @@ -1,122 +1 @@ -GPLed software AS IS, sponsored by 1&1 Internet AG (www.1und1.de). - -Contact: tst@1und1.de - --------------------------------- - -Abstract: - -MARS Light is almost a drop-in replacement for DRBD -(that is, block-level storage replication). - -In contrast to plain DRBD, it works _asynchronously_ and over -arbitrary distances. Our internal 1&1 testing runs between datacenters -in the US and Europe. MARS uses very different technology under the -hood, similar to transaction logging of database systems. - -Reliability: application and replication are completely decoupled. -Networking problems (e.g. packet loss, bottlenecks) have no -impact onto your application at the primary side. - -Anytime Consistency: on a secondary node, its version of the underlying -disk device is always consistent in itself, but may be outdated -(represent a former state from the primary side). Thanks to -incremental replication of the transaction logfiles, usually the -lag-behind will be only a few seconds, or parts of a second. - -Synchronous or near-synchronous operating modes are planned for -the future, but are expected to _reliably_ work only over short -distances (less than 50km), due to fundamental properties -of distributed systems. - -Although many people ask for synchronous modes and although they -would be very easy to implement (basically just add some additional -wait conditions to turn asynchronous IO into synchronous one), I don't -want to implement them for now. - -One reason is DRBD which already does a good job for that ("RAID-1 over -network" which works extremely well on crossover cables). -MARS is no RAID. The transaction logging of MARS is fundamentally -different from that. - -The other reason is that I personally am not convinced by our experiences -with synchronous replication in the presence of network bottlenecks. -Even relatively short bundled 10Gbit lines between datacenters form -a bottleneck where suddenly some unexpected jitter / packet loss may occur, -leading to effects similar to "traffic jam". - -MARS has simply another application area which is different from DRBD. - -WARNING! Current stage is BETA. Don't put productive data on it! - -Documentation: currently under construction, see docu/mars-manual.pdf - -Concepts: - -See later chapters in docu/mars-manual.pdf . - -For a very short intro, see my LCA2013 presentation docu/MARS_LCA2013.pdf . - -There is also an internal 2-years old concept paper which is so much outdated, -that I don't want to publish it. - -The fundamental construction principle of the planned MARS Full -is called Instance Oriented Programming (IOP) and is described in -the following paper: - -http://athomux.net/papers/paper_inst2.pdf - -History: - -As you can see in the git log, it evolved from a very experimental -concept study, starting in the Summer of 2010. -At this time, I was working on it in my spare time. - -In Summer 2011, an "official" internal 1&1 project started, which aimed -to deliver a proof of concept. - -In February 2012, a pilot system was rolled out to an internal statistics -server, which collects statistics data from thousands of other servers, -and thus produces a very heavy random-access write load, formerly -replicated with DRBD (which led to performance problems due to massive -randomness). After switching to MARS, the performance was provably -better. -That server was selected because potential loss of statistics data -would be not be that critical as with other productive data, but -nevertheless it operates on productive data and loads. - -After curing some small infancy problems, that server runs until today -without problems. It was upgraded to newer versions of MARS several -times (indicated by some of the git tags). Our sysadmins switched the -primary side a few times, without informing me, so I could -sleep better at night without knowing what they did ;) - -In Summer 2012, the next "official" internal 1&1 project started. Its goal -is to reach enterprise grade, and therefore to rollout MARS Light on -~15 productive servers, starting with less critical systems like ones -for test webspaces etc. This project will continue until Summer 2013. - -In December 2012 (shortly before Christmas), I got the official permission -from our CTO Henning Kettler to publish MARS under GPL on github. - -Many thanks to him! - -Before that point, I was bound to my working contract which kept internal -software as secret by default (when there was no explicit permission). - -Now there is a chance to build up an opensource -community for MARS, partially outside of 1&1. - -Please contribute! I will be open. - -I also try to respect the guidelines from Linus, but probably this -will need more work. I am already planning to invest some time into -community revision of the sourcecode, but there is not yet any schedule. - -In May 2013, I got help by my new collegue Frank Liepold. He currently -creates a fully automatic test suite which automates regression tests -(goal: rolling releases). That test suite is based on the internal -test suite of blkreplay and will also be published soon. - -Hopefully, there will be an iternal 1&1 followup project for -mass rollout to some thousands of servers. +See http://schoebel.github.io/mars/