[CephFS] Create a CSI volume from a snapshot

[humblec]

Describe the feature you'd like to have

We will be using ceph manager based volume provisioning from v1.1.0. Afaict, we only have a way to create snapshots from a volume. The support for cloning a volume from
existing snapshot looks to be unavailable. This is an important functionality which has to be supported in CSI driver.

This issue tracks this feature support.

[humblec]

@ajarr can you please share your view on this ?

[batrick]

The plan is to have the volumes plugin add a command to recursive copy another subvolume@snapshot to a new subvolume. The interface is still TBD. What do you think?

[humblec]

The plan is to have the volumes plugin add a command to recursive copy another subvolume@snapshot to a new subvolume.

Could you please explain some more on the volume plugin referred here? basically some interface like ceph fs snapshot clone <clonename> <snapname> is what I was proposing. If you were referring same and while invoked internally copying the data recursively to another subvolume is in plan , we are on same page :)

Most of the storage systems has such interface and one example would be gluster as mentioned here https://access.redhat.com/documentation/en-us/red_hat_gluster_storage/3.3/html/administration_guide/ch08s03

[humblec]

@batrick @ajarr Do we have the functionality available today to clone or create a new volume from existing subvol ? afaict, this is not available atm and we need this functionality too.

[ajarr]

@humblec , no. not available atm.

[humblec]

@humblec , no. not available atm.

Thanks for confirming, we need this functionality too.

[batrick]

The plan is to have the volumes plugin add a command to recursive copy another subvolume@snapshot to a new subvolume.

Could you please explain some more on the volume plugin referred here?

The ceph-mgr "volumes" plugin that @ajarr is working on.

basically some interface like ceph fs snapshot clone <clonename> <snapname> is what I was proposing. If you were referring same and while invoked internally copying the data recursively to another subvolume is in plan , we are on same page :)

It would probably look like ceph fs subvolume clone <vol> <subvol> <snapshot> <new_subvol>. @ajarr ?

[humblec]

The ceph-mgr "volumes" plugin that @ajarr is working on.

Oh. OK, thanks for clarifying.

ceph fs subvolume clone <vol> <subvol> <snapshot> <new_subvol>

Does above command can be reused, if we want to clone a subvol from an existing one ? or is the plan to do it with a seperate command?. If ceph fs subvolume clone is the first strings, may be its good to accommodate that functionality too in the same, Isnt it ? @batrick @ajarr

[tombarron]

We'd like to be able to use this directly from the OpenStack Manila driver as well. This would enable both (1) Manila CephFS (and CephFS with NFS) create-share-from snapshot support, and (2) manila-CSI (recently merged by gman0 in k8s/cloud-provider-openstack) support for creating a new volume from snapshot.

[ShyamsundarR]

The plan is to have the volumes plugin add a command to recursive copy another subvolume@snapshot to a new subvolume. The interface is still TBD. What do you think?

A clone in CSI is created using the CreateVolume call, with a VolumeContentSource as the snapshot to clone from. If we perform a recursive copy of data when such a CreateVolume is invoked, it would very likely take time, causing the caller to time out on the CreateVolume call, and try again.

The ceph-csi behaviour in this case would be, for the subsequent retries, to block on a mutex that the first call still holds. Thus delaying a response to the retry as well (based on time taken to copy).

I see that the container orchestrator, would possibly retry this call a few times, depending on the time taken to copy the data. Also, the time it would take is not deterministic. This sounds like a poor choice to implement this feature. I would hence ask what the urgency is to implement clone for CephFS subvolumes and if we should really be waiting for native clone support from CephFS instead?