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diff --git a/doc/cephfs/health-messages.rst b/doc/cephfs/health-messages.rst new file mode 100644 index 000000000..28ceb704a --- /dev/null +++ b/doc/cephfs/health-messages.rst @@ -0,0 +1,170 @@ + +.. _cephfs-health-messages: + +====================== +CephFS health messages +====================== + +Cluster health checks +===================== + +The Ceph monitor daemons will generate health messages in response +to certain states of the file system map structure (and the enclosed MDS maps). + +Message: mds rank(s) *ranks* have failed +Description: One or more MDS ranks are not currently assigned to +an MDS daemon; the cluster will not recover until a suitable replacement +daemon starts. + +Message: mds rank(s) *ranks* are damaged +Description: One or more MDS ranks has encountered severe damage to +its stored metadata, and cannot start again until it is repaired. + +Message: mds cluster is degraded +Description: One or more MDS ranks are not currently up and running, clients +may pause metadata IO until this situation is resolved. This includes +ranks being failed or damaged, and additionally includes ranks +which are running on an MDS but have not yet made it to the *active* +state (e.g. ranks currently in *replay* state). + +Message: mds *names* are laggy +Description: The named MDS daemons have failed to send beacon messages +to the monitor for at least ``mds_beacon_grace`` (default 15s), while +they are supposed to send beacon messages every ``mds_beacon_interval`` +(default 4s). The daemons may have crashed. The Ceph monitor will +automatically replace laggy daemons with standbys if any are available. + +Message: insufficient standby daemons available +Description: One or more file systems are configured to have a certain number +of standby daemons available (including daemons in standby-replay) but the +cluster does not have enough standby daemons. The standby daemons not in replay +count towards any file system (i.e. they may overlap). This warning can +configured by setting ``ceph fs set <fs> standby_count_wanted <count>``. Use +zero for ``count`` to disable. + + +Daemon-reported health checks +============================= + +MDS daemons can identify a variety of unwanted conditions, and +indicate these to the operator in the output of ``ceph status``. +These conditions have human readable messages, and additionally +a unique code starting with ``MDS_``. + +.. highlight:: console + +``ceph health detail`` shows the details of the conditions. Following +is a typical health report from a cluster experiencing MDS related +performance issues:: + + $ ceph health detail + HEALTH_WARN 1 MDSs report slow metadata IOs; 1 MDSs report slow requests + MDS_SLOW_METADATA_IO 1 MDSs report slow metadata IOs + mds.fs-01(mds.0): 3 slow metadata IOs are blocked > 30 secs, oldest blocked for 51123 secs + MDS_SLOW_REQUEST 1 MDSs report slow requests + mds.fs-01(mds.0): 5 slow requests are blocked > 30 secs + +Where, for intance, ``MDS_SLOW_REQUEST`` is the unique code representing the +condition where requests are taking long time to complete. And the following +description shows its severity and the MDS daemons which are serving these +slow requests. + +This page lists the health checks raised by MDS daemons. For the checks from +other daemons, please see :ref:`health-checks`. + +* ``MDS_TRIM`` + + Message + "Behind on trimming..." + Description + CephFS maintains a metadata journal that is divided into + *log segments*. The length of journal (in number of segments) is controlled + by the setting ``mds_log_max_segments``, and when the number of segments + exceeds that setting the MDS starts writing back metadata so that it + can remove (trim) the oldest segments. If this writeback is happening + too slowly, or a software bug is preventing trimming, then this health + message may appear. The threshold for this message to appear is controlled by + the config option ``mds_log_warn_factor``, the default is 2.0. +* ``MDS_HEALTH_CLIENT_LATE_RELEASE``, ``MDS_HEALTH_CLIENT_LATE_RELEASE_MANY`` + + Message + "Client *name* failing to respond to capability release" + Description + CephFS clients are issued *capabilities* by the MDS, which + are like locks. Sometimes, for example when another client needs access, + the MDS will request clients release their capabilities. If the client + is unresponsive or buggy, it might fail to do so promptly or fail to do + so at all. This message appears if a client has taken longer than + ``session_timeout`` (default 60s) to comply. +* ``MDS_CLIENT_RECALL``, ``MDS_HEALTH_CLIENT_RECALL_MANY`` + + Message + "Client *name* failing to respond to cache pressure" + Description + Clients maintain a metadata cache. Items (such as inodes) in the + client cache are also pinned in the MDS cache, so when the MDS needs to shrink + its cache (to stay within ``mds_cache_memory_limit``), it sends messages to + clients to shrink their caches too. If the client is unresponsive or buggy, + this can prevent the MDS from properly staying within its cache limits and it + may eventually run out of memory and crash. This message appears if a client + has failed to release more than + ``mds_recall_warning_threshold`` capabilities (decaying with a half-life of + ``mds_recall_max_decay_rate``) within the last + ``mds_recall_warning_decay_rate`` second. +* ``MDS_CLIENT_OLDEST_TID``, ``MDS_CLIENT_OLDEST_TID_MANY`` + + Message + "Client *name* failing to advance its oldest client/flush tid" + Description + The CephFS client-MDS protocol uses a field called the + *oldest tid* to inform the MDS of which client requests are fully + complete and may therefore be forgotten about by the MDS. If a buggy + client is failing to advance this field, then the MDS may be prevented + from properly cleaning up resources used by client requests. This message + appears if a client appears to have more than ``max_completed_requests`` + (default 100000) requests that are complete on the MDS side but haven't + yet been accounted for in the client's *oldest tid* value. +* ``MDS_DAMAGE`` + + Message + "Metadata damage detected" + Description + Corrupt or missing metadata was encountered when reading + from the metadata pool. This message indicates that the damage was + sufficiently isolated for the MDS to continue operating, although + client accesses to the damaged subtree will return IO errors. Use + the ``damage ls`` admin socket command to get more detail on the damage. + This message appears as soon as any damage is encountered. +* ``MDS_HEALTH_READ_ONLY`` + + Message + "MDS in read-only mode" + Description + The MDS has gone into readonly mode and will return EROFS + error codes to client operations that attempt to modify any metadata. The + MDS will go into readonly mode if it encounters a write error while + writing to the metadata pool, or if forced to by an administrator using + the *force_readonly* admin socket command. +* ``MDS_SLOW_REQUEST`` + + Message + "*N* slow requests are blocked" + + Description + One or more client requests have not been completed promptly, + indicating that the MDS is either running very slowly, or that the RADOS + cluster is not acknowledging journal writes promptly, or that there is a bug. + Use the ``ops`` admin socket command to list outstanding metadata operations. + This message appears if any client requests have taken longer than + ``mds_op_complaint_time`` (default 30s). +* ``MDS_CACHE_OVERSIZED`` + + Message + "Too many inodes in cache" + Description + The MDS is not succeeding in trimming its cache to comply with the + limit set by the administrator. If the MDS cache becomes too large, the daemon + may exhaust available memory and crash. By default, this message appears if + the actual cache size (in memory) is at least 50% greater than + ``mds_cache_memory_limit`` (default 1GB). Modify ``mds_health_cache_threshold`` + to set the warning ratio. |