mirror of https://github.com/ceph/ceph
211 lines
8.4 KiB
ReStructuredText
211 lines
8.4 KiB
ReStructuredText
=================
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Troubleshooting
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=================
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Slow/stuck operations
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=====================
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If you are experiencing apparent hung operations, the first task is to identify
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where the problem is occurring: in the client, the MDS, or the network connecting
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them. Start by looking to see if either side has stuck operations
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(:ref:`slow_requests`, below), and narrow it down from there.
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We can get hints about what's going on by dumping the MDS cache ::
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ceph daemon mds.<name> dump cache /tmp/dump.txt
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.. note:: The file `dump.txt` is on the machine executing the MDS and for systemd
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controlled MDS services, this is in a tmpfs in the MDS container.
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Use `nsenter(1)` to locate `dump.txt` or specify another system-wide path.
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If high logging levels are set on the MDS, that will almost certainly hold the
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information we need to diagnose and solve the issue.
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RADOS Health
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============
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If part of the CephFS metadata or data pools is unavailable and CephFS is not
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responding, it is probably because RADOS itself is unhealthy. Resolve those
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problems first (:doc:`../../rados/troubleshooting/index`).
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The MDS
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=======
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If an operation is hung inside the MDS, it will eventually show up in ``ceph health``,
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identifying "slow requests are blocked". It may also identify clients as
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"failing to respond" or misbehaving in other ways. If the MDS identifies
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specific clients as misbehaving, you should investigate why they are doing so.
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Generally it will be the result of
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#. Overloading the system (if you have extra RAM, increase the
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"mds cache memory limit" config from its default 1GiB; having a larger active
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file set than your MDS cache is the #1 cause of this!).
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#. Running an older (misbehaving) client.
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#. Underlying RADOS issues.
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Otherwise, you have probably discovered a new bug and should report it to
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the developers!
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.. _slow_requests:
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Slow requests (MDS)
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-------------------
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You can list current operations via the admin socket by running::
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ceph daemon mds.<name> dump_ops_in_flight
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from the MDS host. Identify the stuck commands and examine why they are stuck.
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Usually the last "event" will have been an attempt to gather locks, or sending
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the operation off to the MDS log. If it is waiting on the OSDs, fix them. If
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operations are stuck on a specific inode, you probably have a client holding
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caps which prevent others from using it, either because the client is trying
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to flush out dirty data or because you have encountered a bug in CephFS'
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distributed file lock code (the file "capabilities" ["caps"] system).
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If it's a result of a bug in the capabilities code, restarting the MDS
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is likely to resolve the problem.
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If there are no slow requests reported on the MDS, and it is not reporting
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that clients are misbehaving, either the client has a problem or its
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requests are not reaching the MDS.
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.. _ceph_fuse_debugging:
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ceph-fuse debugging
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===================
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ceph-fuse also supports ``dump_ops_in_flight``. See if it has any and where they are
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stuck.
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Debug output
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------------
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To get more debugging information from ceph-fuse, try running in the foreground
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with logging to the console (``-d``) and enabling client debug
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(``--debug-client=20``), enabling prints for each message sent
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(``--debug-ms=1``).
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If you suspect a potential monitor issue, enable monitor debugging as well
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(``--debug-monc=20``).
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.. _kernel_mount_debugging:
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Kernel mount debugging
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======================
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If there is an issue with the kernel client, the most important thing is
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figuring out whether the problem is with the kernel client or the MDS. Generally,
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this is easy to work out. If the kernel client broke directly, there will be
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output in ``dmesg``. Collect it and any inappropriate kernel state.
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Slow requests
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-------------
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Unfortunately the kernel client does not support the admin socket, but it has
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similar (if limited) interfaces if your kernel has debugfs enabled. There
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will be a folder in ``sys/kernel/debug/ceph/``, and that folder (whose name will
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look something like ``28f7427e-5558-4ffd-ae1a-51ec3042759a.client25386880``)
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will contain a variety of files that output interesting output when you ``cat``
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them. These files are described below; the most interesting when debugging
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slow requests are probably the ``mdsc`` and ``osdc`` files.
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* bdi: BDI info about the Ceph system (blocks dirtied, written, etc)
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* caps: counts of file "caps" structures in-memory and used
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* client_options: dumps the options provided to the CephFS mount
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* dentry_lru: Dumps the CephFS dentries currently in-memory
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* mdsc: Dumps current requests to the MDS
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* mdsmap: Dumps the current MDSMap epoch and MDSes
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* mds_sessions: Dumps the current sessions to MDSes
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* monc: Dumps the current maps from the monitor, and any "subscriptions" held
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* monmap: Dumps the current monitor map epoch and monitors
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* osdc: Dumps the current ops in-flight to OSDs (ie, file data IO)
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* osdmap: Dumps the current OSDMap epoch, pools, and OSDs
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If there are no stuck requests but you have file IO which is not progressing,
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you might have a...
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Disconnected+Remounted FS
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=========================
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Because CephFS has a "consistent cache", if your network connection is
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disrupted for a long enough time, the client will be forcibly
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disconnected from the system. At this point, the kernel client is in
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a bind: it cannot safely write back dirty data, and many applications
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do not handle IO errors correctly on close().
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At the moment, the kernel client will remount the FS, but outstanding file system
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IO may or may not be satisfied. In these cases, you may need to reboot your
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client system.
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You can identify you are in this situation if dmesg/kern.log report something like::
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Jul 20 08:14:38 teuthology kernel: [3677601.123718] ceph: mds0 closed our session
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Jul 20 08:14:38 teuthology kernel: [3677601.128019] ceph: mds0 reconnect start
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Jul 20 08:14:39 teuthology kernel: [3677602.093378] ceph: mds0 reconnect denied
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Jul 20 08:14:39 teuthology kernel: [3677602.098525] ceph: dropping dirty+flushing Fw state for ffff8802dc150518 1099935956631
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Jul 20 08:14:39 teuthology kernel: [3677602.107145] ceph: dropping dirty+flushing Fw state for ffff8801008e8518 1099935946707
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Jul 20 08:14:39 teuthology kernel: [3677602.196747] libceph: mds0 172.21.5.114:6812 socket closed (con state OPEN)
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Jul 20 08:14:40 teuthology kernel: [3677603.126214] libceph: mds0 172.21.5.114:6812 connection reset
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Jul 20 08:14:40 teuthology kernel: [3677603.132176] libceph: reset on mds0
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This is an area of ongoing work to improve the behavior. Kernels will soon
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be reliably issuing error codes to in-progress IO, although your application(s)
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may not deal with them well. In the longer-term, we hope to allow reconnect
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and reclaim of data in cases where it won't violate POSIX semantics (generally,
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data which hasn't been accessed or modified by other clients).
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Mounting
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========
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Mount 5 Error
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-------------
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A mount 5 error typically occurs if a MDS server is laggy or if it crashed.
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Ensure at least one MDS is up and running, and the cluster is ``active +
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healthy``.
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Mount 12 Error
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--------------
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A mount 12 error with ``cannot allocate memory`` usually occurs if you have a
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version mismatch between the :term:`Ceph Client` version and the :term:`Ceph
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Storage Cluster` version. Check the versions using::
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ceph -v
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If the Ceph Client is behind the Ceph cluster, try to upgrade it::
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sudo apt-get update && sudo apt-get install ceph-common
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You may need to uninstall, autoclean and autoremove ``ceph-common``
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and then reinstall it so that you have the latest version.
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Dynamic Debugging
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=================
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You can enable dynamic debug against the CephFS module.
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Please see: https://github.com/ceph/ceph/blob/master/src/script/kcon_all.sh
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Reporting Issues
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================
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If you have identified a specific issue, please report it with as much
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information as possible. Especially important information:
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* Ceph versions installed on client and server
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* Whether you are using the kernel or fuse client
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* If you are using the kernel client, what kernel version?
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* How many clients are in play, doing what kind of workload?
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* If a system is 'stuck', is that affecting all clients or just one?
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* Any ceph health messages
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* Any backtraces in the ceph logs from crashes
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If you are satisfied that you have found a bug, please file it on `the bug
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tracker`. For more general queries, please write to the `ceph-users mailing
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list`.
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.. _the bug tracker: http://tracker.ceph.com
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.. _ceph-users mailing list: http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com/
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