Ceph » CephFS

On a second thought, this feature request should be put on hold until functionality is implemented to revert to an older snapshot quickly. Otherwise, if new snapshots are created while the hystorical ones are not all synced, there will be back-and-forth syncing of the whole diff between the oldest synced snapshot and the current state. If there are no plans to implement the revert functionality, please mark this feature request as invalid.

#69188 should be the way to go until then.

@patrakov @Venky Shankar

I think we could add option(s) to mention the Start Snapshot (Full Sync) and (if necessary) the End Snapshot, so that the user could configure the Sync List based on their business requirement. Wouldn't it resolve these two issues #69187 and #69188?
For example, if we have S1, S2, .... S10. The user could configure the Sync List as {S7, S10} or {S9, S10} based on their urgency. This way, there's no need to implement the reverse order sync. The user could also do {S10, S10} or just use the option --sync-only-the-latest-snapshot. WDYT?

The start snapshot is definitely needed. I don't know if I want the end snapshot or not, so probably not. In other words, I don't see a use case for stopping earlier than the end of the history or for disallowing further mirroring.

The --sync-only-the-latest-snapshot option (when adding a directory) makes sense, as long as subsequent snapshots will also get mirrored. However, the name is ambiguous, so let's make it two options:

• One as a shorthand for starting with the latest snapshot, not mirroring anything earlier, but mirroring all snapshots after that.
• One for starting with the latest snapshot, and, once it is done, mirroring the then-latest snapshot, thus skipping everything in the middle, for the situation where cephfs-mirror is obviously too slow to catch up with every snapshot and thus has to skip, and so on.

Something else that I can think of, in addition to the start snapshot, is a filter for snapshot names based on a positive and a negative regular expression. For example, I would like to disallow mirroring of snapshots that include the word "daily" in their name (as the mirroring will likely spend too much time), or specifically allow it to mirror only snapshots that have the "auto" word in their name.

Alexander Patrakov wrote in #note-4:

The start snapshot is definitely needed. I don't know if I want the end snapshot or not, so probably not. In other words, I don't see a use case for stopping earlier than the end of the history or for disallowing further mirroring.

The --sync-only-the-latest-snapshot option (when adding a directory) makes sense, as long as subsequent snapshots will also get mirrored. However, the name is ambiguous, so let's make it two options:

• One as a shorthand for starting with the latest snapshot, not mirroring anything earlier, but mirroring all snapshots after that.

This new option (let's say --sync-only-the-latest-snapshot) makes sense only when the mirroring of a particular directory is in the off state and the user keep snapshot-ting. Then the user turn on mirroring by 'mirror add'ing the directory using --sync-only-the-latest-snapshot option and it syncs only the latest snapshot of that directory. The sync would be on from that point onwards.

• One for starting with the latest snapshot, and, once it is done, mirroring the then-latest snapshot, thus skipping everything in the middle, for the situation where cephfs-mirror is obviously too slow to catch up with every snapshot and thus has to skip, and so on.

• Take snapshots without adding a directory.
• Turn on mirroring by adding the directory using --sync-only-the-latest-snapshot option.
• Turn it off (remove) and take more snapshots.
• Turn it on using --sync-only-the-latest-snapshot option.

Thus the intermediate snapshots for that directory would be skipped.

Something else that I can think of, in addition to the start snapshot, is a filter for snapshot names based on a positive and a negative regular expression. For example, I would like to disallow mirroring of snapshots that include the word "daily" in their name (as the mirroring will likely spend too much time), or specifically allow it to mirror only snapshots that have the "auto" word in their name.

This would be another enhancement and should be tracked separately.

If we have the first option (--sync-only-the-latest-snapshot), then the user could work it out by:

Take snapshots without adding a directory.
Turn on mirroring by adding the directory using --sync-only-the-latest-snapshot option.
Turn it off (remove) and take more snapshots.
Turn it on using --sync-only-the-latest-snapshot option.

Thus the intermediate snapshots for that directory would be skipped.

This would require changes to the automation that creates the snapshots. I would like to avoid this.

Besides, that automation should not know which snapshots are skipped. It should be decided by cephfs-mirror every time it finishes mirroring a snapshot (which is not the same time as the cron job that creates snapshots runs). Besides, if a user uses the built-in manager support for snapshot schedules (I don't), this suggestion becomes infeasible, because there is no point where a user would be able to insert the "turn on" / "turn off" steps.

In short: I would like to be able to take more automated snapshots than cephfs-mirror can process, as easily as possible and without any mirror-aware scripting, and still have a recent snapshot on the remote side.

@Venky Shankar ping

Alexander Patrakov wrote in #note-6:

If we have the first option (--sync-only-the-latest-snapshot), then the user could work it out by:

Take snapshots without adding a directory.
Turn on mirroring by adding the directory using --sync-only-the-latest-snapshot option.
Turn it off (remove) and take more snapshots.
Turn it on using --sync-only-the-latest-snapshot option.

Thus the intermediate snapshots for that directory would be skipped.

This would require changes to the automation that creates the snapshots. I would like to avoid this.

Besides, that automation should not know which snapshots are skipped. It should be decided by cephfs-mirror every time it finishes mirroring a snapshot (which is not the same time as the cron job that creates snapshots runs). Besides, if a user uses the built-in manager support for snapshot schedules (I don't), this suggestion becomes infeasible, because there is no point where a user would be able to insert the "turn on" / "turn off" steps.

In short: I would like to be able to take more automated snapshots than cephfs-mirror can process, as easily as possible and without any mirror-aware scripting, and still have a recent snapshot on the remote side.

I like the idea in https://tracker.ceph.com/issues/69187#note-4.

@Jos Collin - suggest coming up with the CLI interfaces for the suggested enhancements before starting implementation.

I agree that '--sync-from-snapshot <snap_id>' is the major part of the solution. It does cover all use cases except one, where cephfs-mirror is obviously too slow and the user would like to admit that. I will split this use case out into a separate ticket.