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diff --git a/src/ceph/doc/cephfs/standby.rst b/src/ceph/doc/cephfs/standby.rst deleted file mode 100644 index 6cba2b7..0000000 --- a/src/ceph/doc/cephfs/standby.rst +++ /dev/null @@ -1,222 +0,0 @@ - -Terminology ------------ - -A Ceph cluster may have zero or more CephFS *filesystems*. CephFS -filesystems have a human readable name (set in ``fs new``) -and an integer ID. The ID is called the filesystem cluster ID, -or *FSCID*. - -Each CephFS filesystem has a number of *ranks*, one by default, -which start at zero. A rank may be thought of as a metadata shard. -Controlling the number of ranks in a filesystem is described -in :doc:`/cephfs/multimds` - -Each CephFS ceph-mds process (a *daemon*) initially starts up -without a rank. It may be assigned one by the monitor cluster. -A daemon may only hold one rank at a time. Daemons only give up -a rank when the ceph-mds process stops. - -If a rank is not associated with a daemon, the rank is -considered *failed*. Once a rank is assigned to a daemon, -the rank is considered *up*. - -A daemon has a *name* that is set statically by the administrator -when the daemon is first configured. Typical configurations -use the hostname where the daemon runs as the daemon name. - -Each time a daemon starts up, it is also assigned a *GID*, which -is unique to this particular process lifetime of the daemon. The -GID is an integer. - -Referring to MDS daemons ------------------------- - -Most of the administrative commands that refer to an MDS daemon -accept a flexible argument format that may contain a rank, a GID -or a name. - -Where a rank is used, this may optionally be qualified with -a leading filesystem name or ID. If a daemon is a standby (i.e. -it is not currently assigned a rank), then it may only be -referred to by GID or name. - -For example, if we had an MDS daemon which was called 'myhost', -had GID 5446, and was assigned rank 0 in the filesystem 'myfs' -which had FSCID 3, then any of the following would be suitable -forms of the 'fail' command: - -:: - - ceph mds fail 5446 # GID - ceph mds fail myhost # Daemon name - ceph mds fail 0 # Unqualified rank - ceph mds fail 3:0 # FSCID and rank - ceph mds fail myfs:0 # Filesystem name and rank - -Managing failover ------------------ - -If an MDS daemon stops communicating with the monitor, the monitor will -wait ``mds_beacon_grace`` seconds (default 15 seconds) before marking -the daemon as *laggy*. - -Each file system may specify a number of standby daemons to be considered -healthy. This number includes daemons in standby-replay waiting for a rank to -fail (remember that a standby-replay daemon will not be assigned to take over a -failure for another rank or a failure in a another CephFS file system). The -pool of standby daemons not in replay count towards any file system count. -Each file system may set the number of standby daemons wanted using: - -:: - - ceph fs set <fs name> standby_count_wanted <count> - -Setting ``count`` to 0 will disable the health check. - - -Configuring standby daemons ---------------------------- - -There are four configuration settings that control how a daemon -will behave while in standby: - -:: - - mds_standby_for_name - mds_standby_for_rank - mds_standby_for_fscid - mds_standby_replay - -These may be set in the ceph.conf on the host where the MDS daemon -runs (as opposed to on the monitor). The daemon loads these settings -when it starts, and sends them to the monitor. - -By default, if none of these settings are used, all MDS daemons -which do not hold a rank will be used as standbys for any rank. - -The settings which associate a standby daemon with a particular -name or rank do not guarantee that the daemon will *only* be used -for that rank. They mean that when several standbys are available, -the associated standby daemon will be used. If a rank is failed, -and a standby is available, it will be used even if it is associated -with a different rank or named daemon. - -mds_standby_replay -~~~~~~~~~~~~~~~~~~ - -If this is set to true, then the standby daemon will continuously read -the metadata journal of an up rank. This will give it -a warm metadata cache, and speed up the process of failing over -if the daemon serving the rank fails. - -An up rank may only have one standby replay daemon assigned to it, -if two daemons are both set to be standby replay then one of them -will arbitrarily win, and the other will become a normal non-replay -standby. - -Once a daemon has entered the standby replay state, it will only be -used as a standby for the rank that it is following. If another rank -fails, this standby replay daemon will not be used as a replacement, -even if no other standbys are available. - -*Historical note:* In Ceph prior to v10.2.1, this setting (when ``false``) is -always true when ``mds_standby_for_*`` is also set. - -mds_standby_for_name -~~~~~~~~~~~~~~~~~~~~ - -Set this to make the standby daemon only take over a failed rank -if the last daemon to hold it matches this name. - -mds_standby_for_rank -~~~~~~~~~~~~~~~~~~~~ - -Set this to make the standby daemon only take over the specified -rank. If another rank fails, this daemon will not be used to -replace it. - -Use in conjunction with ``mds_standby_for_fscid`` to be specific -about which filesystem's rank you are targeting, if you have -multiple filesystems. - -mds_standby_for_fscid -~~~~~~~~~~~~~~~~~~~~~ - -If ``mds_standby_for_rank`` is set, this is simply a qualifier to -say which filesystem's rank is referred to. - -If ``mds_standby_for_rank`` is not set, then setting FSCID will -cause this daemon to target any rank in the specified FSCID. Use -this if you have a daemon that you want to use for any rank, but -only within a particular filesystem. - -mon_force_standby_active -~~~~~~~~~~~~~~~~~~~~~~~~ - -This setting is used on monitor hosts. It defaults to true. - -If it is false, then daemons configured with standby_replay=true -will **only** become active if the rank/name that they have -been configured to follow fails. On the other hand, if this -setting is true, then a daemon configured with standby_replay=true -may be assigned some other rank. - -Examples --------- - -These are example ceph.conf snippets. In practice you can either -copy a ceph.conf with all daemons' configuration to all your servers, -or you can have a different file on each server that contains just -that server's daemons' configuration. - -Simple pair -~~~~~~~~~~~ - -Two MDS daemons 'a' and 'b' acting as a pair, where whichever one is not -currently assigned a rank will be the standby replay follower -of the other. - -:: - - [mds.a] - mds standby replay = true - mds standby for rank = 0 - - [mds.b] - mds standby replay = true - mds standby for rank = 0 - -Floating standby -~~~~~~~~~~~~~~~~ - -Three MDS daemons 'a', 'b' and 'c', in a filesystem that has -``max_mds`` set to 2. - -:: - - # No explicit configuration required: whichever daemon is - # not assigned a rank will go into 'standby' and take over - # for whichever other daemon fails. - -Two MDS clusters -~~~~~~~~~~~~~~~~ - -With two filesystems, I have four MDS daemons, and I want two -to act as a pair for one filesystem and two to act as a pair -for the other filesystem. - -:: - - [mds.a] - mds standby for fscid = 1 - - [mds.b] - mds standby for fscid = 1 - - [mds.c] - mds standby for fscid = 2 - - [mds.d] - mds standby for fscid = 2 - |