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diff --git a/doc/cephfs/snap-schedule.rst b/doc/cephfs/snap-schedule.rst new file mode 100644 index 000000000..2b8873699 --- /dev/null +++ b/doc/cephfs/snap-schedule.rst @@ -0,0 +1,209 @@ +.. _snap-schedule: + +========================== +Snapshot Scheduling Module +========================== +This module implements scheduled snapshots for CephFS. +It provides a user interface to add, query and remove snapshots schedules and +retention policies, as well as a scheduler that takes the snapshots and prunes +existing snapshots accordingly. + + +How to enable +============= + +The *snap_schedule* module is enabled with:: + + ceph mgr module enable snap_schedule + +Usage +===== + +This module uses :doc:`/dev/cephfs-snapshots`, please consider this documentation +as well. + +This module's subcommands live under the `ceph fs snap-schedule` namespace. +Arguments can either be supplied as positional arguments or as keyword +arguments. Once a keyword argument was encountered, all following arguments are +assumed to be keyword arguments too. + +Snapshot schedules are identified by path, their repeat interval and their start +time. The +repeat interval defines the time between two subsequent snapshots. It is +specified by a number and a period multiplier, one of `h(our)`, `d(ay)` and +`w(eek)`. E.g. a repeat interval of `12h` specifies one snapshot every 12 +hours. +The start time is specified as a time string (more details about passing times +below). By default +the start time is last midnight. So when a snapshot schedule with repeat +interval `1h` is added at 13:50 +with the default start time, the first snapshot will be taken at 14:00. +The time zone is assumed to be UTC if none is explicitly included in the string. +An explicit time zone will be mapped to UTC at execution. +The start time must be in ISO8601 format. Examples below: + +UTC: 2022-08-08T05:30:00 i.e. 5:30 AM UTC, without explicit time zone offset +IDT: 2022-08-08T09:00:00+03:00 i.e. 6:00 AM UTC +EDT: 2022-08-08T05:30:00-04:00 i.e. 9:30 AM UTC + +Retention specifications are identified by path and the retention spec itself. A +retention spec consists of either a number and a time period separated by a +space or concatenated pairs of `<number><time period>`. +The semantics are that a spec will ensure `<number>` snapshots are kept that are +at least `<time period>` apart. For Example `7d` means the user wants to keep 7 +snapshots that are at least one day (but potentially longer) apart from each other. +The following time periods are recognized: `h(our), d(ay), w(eek), m(onth), +y(ear)` and `n`. The latter is a special modifier where e.g. `10n` means keep +the last 10 snapshots regardless of timing, + +All subcommands take optional `fs` argument to specify paths in +multi-fs setups and :doc:`/cephfs/fs-volumes` managed setups. If not +passed `fs` defaults to the first file system listed in the fs_map. +When using :doc:`/cephfs/fs-volumes` the argument `fs` is equivalent to a +`volume`. + +When a timestamp is passed (the `start` argument in the `add`, `remove`, +`activate` and `deactivate` subcommands) the ISO format `%Y-%m-%dT%H:%M:%S` will +always be accepted. When either python3.7 or newer is used or +https://github.com/movermeyer/backports.datetime_fromisoformat is installed, any +valid ISO timestamp that is parsed by python's `datetime.fromisoformat` is valid. + +When no subcommand is supplied a synopsis is printed:: + + #> ceph fs snap-schedule + no valid command found; 8 closest matches: + fs snap-schedule status [<path>] [<fs>] [<format>] + fs snap-schedule list <path> [--recursive] [<fs>] [<format>] + fs snap-schedule add <path> <snap_schedule> [<start>] [<fs>] + fs snap-schedule remove <path> [<repeat>] [<start>] [<fs>] + fs snap-schedule retention add <path> <retention_spec_or_period> [<retention_count>] [<fs>] + fs snap-schedule retention remove <path> <retention_spec_or_period> [<retention_count>] [<fs>] + fs snap-schedule activate <path> [<repeat>] [<start>] [<fs>] + fs snap-schedule deactivate <path> [<repeat>] [<start>] [<fs>] + Error EINVAL: invalid command + +Note: +^^^^^ +A `subvolume` argument is no longer accepted by the commands. + + +Inspect snapshot schedules +-------------------------- + +The module offers two subcommands to inspect existing schedules: `list` and +`status`. Bother offer plain and json output via the optional `format` argument. +The default is plain. +The `list` sub-command will list all schedules on a path in a short single line +format. It offers a `recursive` argument to list all schedules in the specified +directory and all contained directories. +The `status` subcommand prints all available schedules and retention specs for a +path. + +Examples:: + + ceph fs snap-schedule status / + ceph fs snap-schedule status /foo/bar --format=json + ceph fs snap-schedule list / + ceph fs snap-schedule list / --recursive=true # list all schedules in the tree + + +Add and remove schedules +------------------------ +The `add` and `remove` subcommands add and remove snapshots schedules +respectively. Both require at least a `path` argument, `add` additionally +requires a `schedule` argument as described in the USAGE section. + +Multiple different schedules can be added to a path. Two schedules are considered +different from each other if they differ in their repeat interval and their +start time. + +If multiple schedules have been set on a path, `remove` can remove individual +schedules on a path by specifying the exact repeat interval and start time, or +the subcommand can remove all schedules on a path when just a `path` is +specified. + +Examples:: + + ceph fs snap-schedule add / 1h + ceph fs snap-schedule add / 1h 11:55 + ceph fs snap-schedule add / 2h 11:55 + ceph fs snap-schedule remove / 1h 11:55 # removes one single schedule + ceph fs snap-schedule remove / 1h # removes all schedules with --repeat=1h + ceph fs snap-schedule remove / # removes all schedules on path / + +Add and remove retention policies +--------------------------------- +The `retention add` and `retention remove` subcommands allow to manage +retention policies. One path has exactly one retention policy. A policy can +however contain multiple count-time period pairs in order to specify complex +retention policies. +Retention policies can be added and removed individually or in bulk via the +forms `ceph fs snap-schedule retention add <path> <time period> <count>` and +`ceph fs snap-schedule retention add <path> <countTime period>[countTime period]` + +Examples:: + + ceph fs snap-schedule retention add / h 24 # keep 24 snapshots at least an hour apart + ceph fs snap-schedule retention add / d 7 # and 7 snapshots at least a day apart + ceph fs snap-schedule retention remove / h 24 # remove retention for 24 hourlies + ceph fs snap-schedule retention add / 24h4w # add 24 hourly and 4 weekly to retention + ceph fs snap-schedule retention remove / 7d4w # remove 7 daily and 4 weekly, leaves 24 hourly + +.. note: When adding a path to snap-schedule, remember to strip off the mount + point path prefix. Paths to snap-schedule should start at the appropriate + CephFS file system root and not at the host file system root. + e.g. if the Ceph File System is mounted at ``/mnt`` and the path under which + snapshots need to be taken is ``/mnt/some/path`` then the acutal path required + by snap-schedule is only ``/some/path``. + +.. note: It should be noted that the "created" field in the snap-schedule status + command output is the timestamp at which the schedule was created. The "created" + timestamp has nothing to do with the creation of actual snapshots. The actual + snapshot creation is accounted for in the "created_count" field, which is a + cumulative count of the total number of snapshots created so far. + +.. note: The maximum number of snapshots to retain per directory is limited by the + config tunable `mds_max_snaps_per_dir`. This tunable defaults to 100. + To ensure a new snapshot can be created, one snapshot less than this will be + retained. So by default, a maximum of 99 snapshots will be retained. + +.. note: The --fs argument is now required if there is more than one file system. + +Active and inactive schedules +----------------------------- +Snapshot schedules can be added for a path that doesn't exist yet in the +directory tree. Similarly a path can be removed without affecting any snapshot +schedules on that path. +If a directory is not present when a snapshot is scheduled to be taken, the +schedule will be set to inactive and will be excluded from scheduling until +it is activated again. +A schedule can manually be set to inactive to pause the creating of scheduled +snapshots. +The module provides the `activate` and `deactivate` subcommands for this +purpose. + +Examples:: + + ceph fs snap-schedule activate / # activate all schedules on the root directory + ceph fs snap-schedule deactivate / 1d # deactivates daily snapshots on the root directory + +Limitations +----------- +Snapshots are scheduled using python Timers. Under normal circumstances +specifying 1h as the schedule will result in snapshots 1 hour apart fairly +precisely. If the mgr daemon is under heavy load however, the Timer threads +might not get scheduled right away, resulting in a slightly delayed snapshot. If +this happens, the next snapshot will be schedule as if the previous one was not +delayed, i.e. one or more delayed snapshots will not cause drift in the overall +schedule. + +In order to somewhat limit the overall number of snapshots in a file system, the +module will only keep a maximum of 50 snapshots per directory. If the retention +policy results in more then 50 retained snapshots, the retention list will be +shortened to the newest 50 snapshots. + +Data storage +------------ +The snapshot schedule data is stored in a rados object in the cephfs metadata +pool. At runtime all data lives in a sqlite database that is serialized and +stored as a rados object. |