Monitoring a Cluster

After you have a running cluster, you can use the ceph tool to monitor your cluster. Monitoring a cluster typically involves checking OSD status, monitor status, placement group status, and metadata server status.

Using the command line

Interactive mode

To run the ceph tool in interactive mode, type ceph at the command line with no arguments. For example:

ceph
health
status
quorum_status
mon stat

Non-default paths

If you specified non-default locations for your configuration or keyring when you install the cluster, you may specify their locations to the ceph tool by running the following command:

ceph -c /path/to/conf -k /path/to/keyring health

Checking a Cluster’s Status

After you start your cluster, and before you start reading and/or writing data, you should check your cluster’s status.

To check a cluster’s status, run the following command:

ceph status

Alternatively, you can run the following command:

ceph -s

In interactive mode, this operation is performed by typing status and pressing Enter:

status

Ceph will print the cluster status. For example, a tiny Ceph “demonstration cluster” that is running one instance of each service (monitor, manager, and OSD) might print the following:

cluster:
  id:     477e46f1-ae41-4e43-9c8f-72c918ab0a20
  health: HEALTH_OK

services:
  mon: 3 daemons, quorum a,b,c
  mgr: x(active)
  mds: cephfs_a-1/1/1 up  {0=a=up:active}, 2 up:standby
  osd: 3 osds: 3 up, 3 in

data:
  pools:   2 pools, 16 pgs
  objects: 21 objects, 2.19K
  usage:   546 GB used, 384 GB / 931 GB avail
  pgs:     16 active+clean

How Ceph Calculates Data Usage

The usage value reflects the actual amount of raw storage used. The xxx GB / xxx GB value means the amount available (the lesser number) of the overall storage capacity of the cluster. The notional number reflects the size of the stored data before it is replicated, cloned or snapshotted. Therefore, the amount of data actually stored typically exceeds the notional amount stored, because Ceph creates replicas of the data and may also use storage capacity for cloning and snapshotting.

Watching a Cluster

Each daemon in the Ceph cluster maintains a log of events, and the Ceph cluster itself maintains a cluster log that records high-level events about the entire Ceph cluster. These events are logged to disk on monitor servers (in the default location /var/log/ceph/ceph.log), and they can be monitored via the command line.

To follow the cluster log, run the following command:

ceph -w

Ceph will print the status of the system, followed by each log message as it is added. For example:

cluster:
  id:     477e46f1-ae41-4e43-9c8f-72c918ab0a20
  health: HEALTH_OK

services:
  mon: 3 daemons, quorum a,b,c
  mgr: x(active)
  mds: cephfs_a-1/1/1 up  {0=a=up:active}, 2 up:standby
  osd: 3 osds: 3 up, 3 in

data:
  pools:   2 pools, 16 pgs
  objects: 21 objects, 2.19K
  usage:   546 GB used, 384 GB / 931 GB avail
  pgs:     16 active+clean


2017-07-24 08:15:11.329298 mon.a mon.0 172.21.9.34:6789/0 23 : cluster [INF] osd.0 172.21.9.34:6806/20527 boot
2017-07-24 08:15:14.258143 mon.a mon.0 172.21.9.34:6789/0 39 : cluster [INF] Activating manager daemon x
2017-07-24 08:15:15.446025 mon.a mon.0 172.21.9.34:6789/0 47 : cluster [INF] Manager daemon x is now available

Instead of printing log lines as they are added, you might want to print only the most recent lines. Run ceph log last [n] to see the most recent n lines from the cluster log.

Monitoring Health Checks

Ceph continuously runs various health checks. When a health check fails, this failure is reflected in the output of ceph status and ceph health. The cluster log receives messages that indicate when a check has failed and when the cluster has recovered.

For example, when an OSD goes down, the health section of the status output is updated as follows:

health: HEALTH_WARN
        1 osds down
        Degraded data redundancy: 21/63 objects degraded (33.333%), 16 pgs unclean, 16 pgs degraded

At the same time, cluster log messages are emitted to record the failure of the health checks:

2017-07-25 10:08:58.265945 mon.a mon.0 172.21.9.34:6789/0 91 : cluster [WRN] Health check failed: 1 osds down (OSD_DOWN)
2017-07-25 10:09:01.302624 mon.a mon.0 172.21.9.34:6789/0 94 : cluster [WRN] Health check failed: Degraded data redundancy: 21/63 objects degraded (33.333%), 16 pgs unclean, 16 pgs degraded (PG_DEGRADED)

When the OSD comes back online, the cluster log records the cluster’s return to a healthy state:

2017-07-25 10:11:11.526841 mon.a mon.0 172.21.9.34:6789/0 109 : cluster [WRN] Health check update: Degraded data redundancy: 2 pgs unclean, 2 pgs degraded, 2 pgs undersized (PG_DEGRADED)
2017-07-25 10:11:13.535493 mon.a mon.0 172.21.9.34:6789/0 110 : cluster [INF] Health check cleared: PG_DEGRADED (was: Degraded data redundancy: 2 pgs unclean, 2 pgs degraded, 2 pgs undersized)
2017-07-25 10:11:13.535577 mon.a mon.0 172.21.9.34:6789/0 111 : cluster [INF] Cluster is now healthy

Network Performance Checks

Ceph OSDs send heartbeat ping messages to each other in order to monitor daemon availability and network performance. If a single delayed response is detected, this might indicate nothing more than a busy OSD. But if multiple delays between distinct pairs of OSDs are detected, this might indicate a failed network switch, a NIC failure, or a layer 1 failure.

By default, a heartbeat time that exceeds 1 second (1000 milliseconds) raises a health check (a HEALTH_WARN. For example:

HEALTH_WARN Slow OSD heartbeats on back (longest 1118.001ms)

In the output of the ceph health detail command, you can see which OSDs are experiencing delays and how long the delays are. The output of ceph health detail is limited to ten lines. Here is an example of the output you can expect from the ceph health detail command:

[WRN] OSD_SLOW_PING_TIME_BACK: Slow OSD heartbeats on back (longest 1118.001ms)
    Slow OSD heartbeats on back from osd.0 [dc1,rack1] to osd.1 [dc1,rack1] 1118.001 msec possibly improving
    Slow OSD heartbeats on back from osd.0 [dc1,rack1] to osd.2 [dc1,rack2] 1030.123 msec
    Slow OSD heartbeats on back from osd.2 [dc1,rack2] to osd.1 [dc1,rack1] 1015.321 msec
    Slow OSD heartbeats on back from osd.1 [dc1,rack1] to osd.0 [dc1,rack1] 1010.456 msec

To see more detail and to collect a complete dump of network performance information, use the dump_osd_network command. This command is usually sent to a Ceph Manager Daemon, but it can be used to collect information about a specific OSD’s interactions by sending it to that OSD. The default threshold for a slow heartbeat is 1 second (1000 milliseconds), but this can be overridden by providing a number of milliseconds as an argument.

To show all network performance data with a specified threshold of 0, send the following command to the mgr:

ceph daemon /var/run/ceph/ceph-mgr.x.asok dump_osd_network 0
{
    "threshold": 0,
    "entries": [
        {
            "last update": "Wed Sep  4 17:04:49 2019",
            "stale": false,
            "from osd": 2,
            "to osd": 0,
            "interface": "front",
            "average": {
                "1min": 1.023,
                "5min": 0.860,
                "15min": 0.883
            },
            "min": {
                "1min": 0.818,
                "5min": 0.607,
                "15min": 0.607
            },
            "max": {
                "1min": 1.164,
                "5min": 1.173,
                "15min": 1.544
            },
            "last": 0.924
        },
        {
            "last update": "Wed Sep  4 17:04:49 2019",
            "stale": false,
            "from osd": 2,
            "to osd": 0,
            "interface": "back",
            "average": {
                "1min": 0.968,
                "5min": 0.897,
                "15min": 0.830
            },
            "min": {
                "1min": 0.860,
                "5min": 0.563,
                "15min": 0.502
            },
            "max": {
                "1min": 1.171,
                "5min": 1.216,
                "15min": 1.456
            },
            "last": 0.845
        },
        {
            "last update": "Wed Sep  4 17:04:48 2019",
            "stale": false,
            "from osd": 0,
            "to osd": 1,
            "interface": "front",
            "average": {
                "1min": 0.965,
                "5min": 0.811,
                "15min": 0.850
            },
            "min": {
                "1min": 0.650,
                "5min": 0.488,
                "15min": 0.466
            },
            "max": {
                "1min": 1.252,
                "5min": 1.252,
                "15min": 1.362
            },
        "last": 0.791
    },
    ...

Muting Health Checks

Health checks can be muted so that they have no effect on the overall reported status of the cluster. For example, if the cluster has raised a single health check and then you mute that health check, then the cluster will report a status of HEALTH_OK. To mute a specific health check, use the health check code that corresponds to that health check (see Health checks), and run the following command:

ceph health mute <code>

For example, to mute an OSD_DOWN health check, run the following command:

ceph health mute OSD_DOWN

Mutes are reported as part of the short and long form of the ceph health command’s output. For example, in the above scenario, the cluster would report:

ceph health
HEALTH_OK (muted: OSD_DOWN)
ceph health detail
HEALTH_OK (muted: OSD_DOWN)
(MUTED) OSD_DOWN 1 osds down
    osd.1 is down

A mute can be removed by running the following command:

ceph health unmute <code>

For example:

ceph health unmute OSD_DOWN

A “health mute” can have a TTL (Time To Live) associated with it: this means that the mute will automatically expire after a specified period of time. The TTL is specified as an optional duration argument, as seen in the following examples:

ceph health mute OSD_DOWN 4h    # mute for 4 hours
ceph health mute MON_DOWN 15m   # mute for 15 minutes

Normally, if a muted health check is resolved (for example, if the OSD that raised the OSD_DOWN health check in the example above has come back up), the mute goes away. If the health check comes back later, it will be reported in the usual way.

It is possible to make a health mute “sticky”: this means that the mute will remain even if the health check clears. For example, to make a health mute “sticky”, you might run the following command:

ceph health mute OSD_DOWN 1h --sticky   # ignore any/all down OSDs for next hour

Most health mutes disappear if the unhealthy condition that triggered the health check gets worse. For example, suppose that there is one OSD down and the health check is muted. In that case, if one or more additional OSDs go down, then the health mute disappears. This behavior occurs in any health check with a threshold value.

Checking a Cluster’s Usage Stats

To check a cluster’s data usage and data distribution among pools, use the df command. This option is similar to Linux’s df command. Run the following command:

ceph df

The output of ceph df resembles the following:

CLASS     SIZE    AVAIL     USED  RAW USED  %RAW USED
ssd    202 GiB  200 GiB  2.0 GiB   2.0 GiB       1.00
TOTAL  202 GiB  200 GiB  2.0 GiB   2.0 GiB       1.00

--- POOLS ---
POOL                   ID  PGS   STORED   (DATA)   (OMAP)   OBJECTS     USED  (DATA)   (OMAP)   %USED  MAX AVAIL  QUOTA OBJECTS  QUOTA BYTES  DIRTY  USED COMPR  UNDER COMPR
device_health_metrics   1    1  242 KiB   15 KiB  227 KiB         4  251 KiB  24 KiB  227 KiB       0    297 GiB            N/A          N/A      4         0 B          0 B
cephfs.a.meta           2   32  6.8 KiB  6.8 KiB      0 B        22   96 KiB  96 KiB      0 B       0    297 GiB            N/A          N/A     22         0 B          0 B
cephfs.a.data           3   32      0 B      0 B      0 B         0      0 B     0 B      0 B       0     99 GiB            N/A          N/A      0         0 B          0 B
test                    4   32   22 MiB   22 MiB   50 KiB       248   19 MiB  19 MiB   50 KiB       0    297 GiB            N/A          N/A    248         0 B          0 B
  • CLASS: For example, “ssd” or “hdd”.

  • SIZE: The amount of storage capacity managed by the cluster.

  • AVAIL: The amount of free space available in the cluster.

  • USED: The amount of raw storage consumed by user data (excluding BlueStore’s database).

  • RAW USED: The amount of raw storage consumed by user data, internal overhead, and reserved capacity.

  • %RAW USED: The percentage of raw storage used. Watch this number in conjunction with full ratio and near full ratio to be forewarned when your cluster approaches the fullness thresholds. See Storage Capacity.

POOLS:

The POOLS section of the output provides a list of pools and the notional usage of each pool. This section of the output DOES NOT reflect replicas, clones, or snapshots. For example, if you store an object with 1MB of data, then the notional usage will be 1MB, but the actual usage might be 2MB or more depending on the number of replicas, clones, and snapshots.

  • ID: The number of the specific node within the pool.

  • STORED: The actual amount of data that the user has stored in a pool. This is similar to the USED column in earlier versions of Ceph, but the calculations (for BlueStore!) are more precise (in that gaps are properly handled).

    • (DATA): Usage for RBD (RADOS Block Device), CephFS file data, and RGW (RADOS Gateway) object data.

    • (OMAP): Key-value pairs. Used primarily by CephFS and RGW (RADOS Gateway) for metadata storage.

  • OBJECTS: The notional number of objects stored per pool (that is, the number of objects other than replicas, clones, or snapshots).

  • USED: The space allocated for a pool over all OSDs. This includes space for replication, space for allocation granularity, and space for the overhead associated with erasure-coding. Compression savings and object-content gaps are also taken into account. However, BlueStore’s database is not included in the amount reported under USED.

    • (DATA): Object usage for RBD (RADOS Block Device), CephFS file data, and RGW (RADOS Gateway) object data.

    • (OMAP): Object key-value pairs. Used primarily by CephFS and RGW (RADOS Gateway) for metadata storage.

  • %USED: The notional percentage of storage used per pool.

  • MAX AVAIL: An estimate of the notional amount of data that can be written to this pool.

  • QUOTA OBJECTS: The number of quota objects.

  • QUOTA BYTES: The number of bytes in the quota objects.

  • DIRTY: The number of objects in the cache pool that have been written to the cache pool but have not yet been flushed to the base pool. This field is available only when cache tiering is in use.

  • USED COMPR: The amount of space allocated for compressed data. This includes compressed data in addition to all of the space required for replication, allocation granularity, and erasure- coding overhead.

  • UNDER COMPR: The amount of data that has passed through compression (summed over all replicas) and that is worth storing in a compressed form.

Note

The numbers in the POOLS section are notional. They do not include the number of replicas, clones, or snapshots. As a result, the sum of the USED and %USED amounts in the POOLS section of the output will not be equal to the sum of the USED and %USED amounts in the RAW section of the output.

Note

The MAX AVAIL value is a complicated function of the replication or the kind of erasure coding used, the CRUSH rule that maps storage to devices, the utilization of those devices, and the configured mon_osd_full_ratio setting.

Checking OSD Status

To check if OSDs are up and in, run the following command:

ceph osd stat

Alternatively, you can run the following command:

ceph osd dump

To view OSDs according to their position in the CRUSH map, run the following command:

ceph osd tree

To print out a CRUSH tree that displays a host, its OSDs, whether the OSDs are up, and the weight of the OSDs, run the following command:

#ID CLASS WEIGHT  TYPE NAME             STATUS REWEIGHT PRI-AFF
 -1       3.00000 pool default
 -3       3.00000 rack mainrack
 -2       3.00000 host osd-host
  0   ssd 1.00000         osd.0             up  1.00000 1.00000
  1   ssd 1.00000         osd.1             up  1.00000 1.00000
  2   ssd 1.00000         osd.2             up  1.00000 1.00000

See Monitoring OSDs and Placement Groups.

Checking Monitor Status

If your cluster has multiple monitors, then you need to perform certain “monitor status” checks. After starting the cluster and before reading or writing data, you should check quorum status. A quorum must be present when multiple monitors are running to ensure proper functioning of your Ceph cluster. Check monitor status regularly in order to ensure that all of the monitors are running.

To display the monitor map, run the following command:

ceph mon stat

Alternatively, you can run the following command:

ceph mon dump

To check the quorum status for the monitor cluster, run the following command:

ceph quorum_status

Ceph returns the quorum status. For example, a Ceph cluster that consists of three monitors might return the following:

{ "election_epoch": 10,
  "quorum": [
        0,
        1,
        2],
  "quorum_names": [
    "a",
    "b",
    "c"],
  "quorum_leader_name": "a",
  "monmap": { "epoch": 1,
      "fsid": "444b489c-4f16-4b75-83f0-cb8097468898",
      "modified": "2011-12-12 13:28:27.505520",
      "created": "2011-12-12 13:28:27.505520",
      "features": {"persistent": [
            "kraken",
            "luminous",
            "mimic"],
    "optional": []
      },
      "mons": [
            { "rank": 0,
              "name": "a",
              "addr": "127.0.0.1:6789/0",
          "public_addr": "127.0.0.1:6789/0"},
            { "rank": 1,
              "name": "b",
              "addr": "127.0.0.1:6790/0",
          "public_addr": "127.0.0.1:6790/0"},
            { "rank": 2,
              "name": "c",
              "addr": "127.0.0.1:6791/0",
          "public_addr": "127.0.0.1:6791/0"}
           ]
  }
}

Checking MDS Status

Metadata servers provide metadata services for CephFS. Metadata servers have two sets of states: up | down and active | inactive. To check if your metadata servers are up and active, run the following command:

ceph mds stat

To display details of the metadata servers, run the following command:

ceph fs dump

Checking Placement Group States

Placement groups (PGs) map objects to OSDs. PGs are monitored in order to ensure that they are active and clean. See Monitoring OSDs and Placement Groups.

Using the Admin Socket

The Ceph admin socket allows you to query a daemon via a socket interface. By default, Ceph sockets reside under /var/run/ceph. To access a daemon via the admin socket, log in to the host that is running the daemon and run one of the two following commands:

ceph daemon {daemon-name}
ceph daemon {path-to-socket-file}

For example, the following commands are equivalent to each other:

ceph daemon osd.0 foo
ceph daemon /var/run/ceph/ceph-osd.0.asok foo

To view the available admin-socket commands, run the following command:

ceph daemon {daemon-name} help

Admin-socket commands enable you to view and set your configuration at runtime. For more on viewing your configuration, see Viewing a Configuration at Runtime. There are two methods of setting configuration value at runtime: (1) using the admin socket, which bypasses the monitor and requires a direct login to the host in question, and (2) using the ceph tell {daemon-type}.{id} config set command, which relies on the monitor and does not require a direct login.