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I have deleted a Ceph filesystem, and copied the metadata and data pools. Is it possible to recreate the filesystem from these copies?

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I can't comment yet due to my reputation, so don't necessarily consider this a full qualified answer.

Since your question is not entirely clear to me, I assume you mean creating a new CephFS containing the pre-existing data?

My short answer is "yes". It depends on various circumstances, of course, but if you have a dump of the data you should be able to create a new filesystem with the same content.

About a year ago we had to recreate our CephFS because of a faulty pool configuration regarding Placement Groups. Since you can't change those settings we had to recreate the whole filesystem. But that went quite smoothly, I can't remember the details but this didn't cause us any trouble. I believe this doesn't even require the metadata. Creating a new CephFS will also create two new pools and then you can replay your data back into the new CephFS.

If you mean to restore the exact same CephFS from the backup data I don't think that's possible because you deleted it. I may be wrong though, you could ask the ceph-users mailing list for further advice.

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  • Thanks for the response, I had almost given up hope! I have the two pools, but for some reason I have run ceph fs rm cephfs cephfs --yes-i-really-mean-it when following a unclear guide. I want to restore the data. The metadata and data pools are intact.
    – Cyclic3
    Oct 10 '18 at 15:04
  • You could try the steps in the ceph disaster guide (docs.ceph.com/docs/mimic/cephfs/disaster-recovery), although I'm not sure it fully applies to your situation when you deleted the fs. Do you have a full backup of the data? If yes, you could just create a new cephfs and replay the data. In any case I would make a copy of those two pools: rados mkpool cephfs-data-recovery rados mkpool cephfs-metadata-recovery rados cppool cephfs_data cephfs-data-recovery rados cppool cephfs_metadata cephfs-metadata-recovery Please ask the mailing list before proceeding.
    – eblock
    Oct 11 '18 at 8:44
  • I have tried the disaster recovery, and the mds keeps getting stuck replaying, or claiming that there is not data available. I'm using an erasure-coded pool for the data. I do have a backup of most of it, so if it is too difficult, to do this I'll just restore from that.
    – Cyclic3
    Oct 11 '18 at 12:04
  • I haven't done this kind of recovery myself yet so you probably should create it from scratch if you don't want to wait until I have time for that ;-)
    – eblock
    Oct 11 '18 at 14:33

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