rbd-mirror: add information about the last snapshot sync to image status

[weirdwiz]

Currently, the rbd mirror status command does not include information about the time taken to sync and bytes in the last snapshot, making it difficult to monitor and troubleshoot the mirroring process. This feature request is to add "last_snapshot_bytes" and "last_snapshot_seconds" fields to the rbd mirror status command, providing administrators with valuable information about the performance of the mirroring process.

Use case:
In snapshot-based mirroring, it's important to know how long it took to sync the last snapshot and how many bytes were transferred during the sync process. This information is useful for monitoring the performance of the mirroring process and identifying any issues that may arise. By adding these fields to the rbd mirror status command, administrators will be able to quickly and easily retrieve this information and use it to optimize the mirroring process.

Fixes: https://tracker.ceph.com/issues/58755

[idryomov]

I'd propose to name the new fields last_snapshot_bytes and last_snapshot_seconds to be closer to existing bytes_per_snapshot and seconds_until_synced fields (and make the units clear -- "time" is is too generic).

[ajarr]

Maybe we need a tracker ticket for this so that it's easier to backport? And that can have more info about the use case.

[idryomov]

Maybe we need a tracker ticket for this so that it's easier to backport?

@weirdwiz Is this done? Please add a link to the commit message as per https://github.com/ceph/ceph/blob/main/SubmittingPatches.rst#id8.

[weirdwiz]

sorry for the delay, there was an issue in my build environment.
@idryomov i tried to make the tracker, but for some reason my account doesn't seem to work correctly.

[idryomov]

sorry for the delay, there was an issue in my build environment.

How was this tested? Can you link some pastes/screenshots show-casing the new fields? last_snapshot_bytes in particular should be equal to the size of the delta that is generated.

@idryomov i tried to make the tracker, but for some reason my account doesn't seem to work correctly.

Please try again now.

[weirdwiz]

I tested it out by writing data to the snapshots using the bench command,

for an empty image,

bin/rbd --cluster site-a bench --io-type write --io-size 64K --io-threads 2 --io-total 4G --io-pattern seq data/image2

status:

{"bytes_per_second":0.0,"bytes_per_snapshot":4294967296.0,"last_sna
pshot_bytes":4294967296,"last_snapshot_seconds":38,"local_snapshot_timestamp":1676612875,"remot
e_snapshot_timestamp":1676612875,"replay_state":"idle"}

wrote 2 gigabytes again to the same image

status:

 {"bytes_per_second":0.0,"bytes_per_snapshot":3221225472.0,"last_snapshot_bytes":2147483648,"last_snapshot_seconds":20,"local_snapshot_timestamp":1676613141,"remot
e_snapshot_timestamp":1676613141,"replay_state":"idle"}

[idryomov]

Fixes: https://tracker.ceph.com/issues/58755

This needs to be added to the commit message too, not just to the description of the PR.

A couple more tweaks are needed

[idryomov]

jenkins test make check

[idryomov]

No related failures:

https://pulpito.ceph.com/dis-2023-02-26_00:02:35-rbd-wip-dis-testing-distro-default-smithi/
https://pulpito.ceph.com/dis-2023-02-26_09:14:25-rbd-wip-dis-testing-distro-default-smithi/