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_.

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 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. The last tid used by the MDS to trim completed client requests (or flush) is included as part of session ls (or client ls) command as a debug aid.

  • 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.

  • MDS_CLIENTS_LAGGY

    Message

    “Client ID is laggy; not evicted because some OSD(s) is/are laggy”

    Description

    If OSD(s) is laggy (due to certain conditions like network cut-off, etc) then it might make clients laggy(session might get idle or cannot flush dirty data for cap revokes). If defer_client_eviction_on_laggy_osds is set to true (default true), client eviction will not take place and thus this health warning will be generated.