Hmm, this is unfortunate news. I don’t think I’ve heard about anything like this before.
Andrej, what Ceph version are you running, and has it changed during this time frame? I would imagine the most likely thing to be our “purge queue” is somehow some times not deleting objects that it marks as removed. But I’ve no idea how that could go wrong. As much information as we can get about stuff like mds restarts during the deletion, single or mult-mds, precise versions, and any pool or file layouts may help narrow things down. (For instance, it may be that the leak only happens if using multiple data pools, or if it was written on a particular version and a later buggy version parses something wrong.) -Greg On Thu, Jul 2, 2026 at 8:53 AM Andras Pataki via ceph-users < [email protected]> wrote: > Hi, > > I have also seen this on a recent large scale/parallel test I can on a > test setup. After creating about a hundred million files, then removing > all of them - there were thousands of objects left in the cephfs data > pool corresponding to inodes that no longer existed. I.e. it looks like > the MDS is "leaking" data - does not correctly delete all objects > corresponding to files in the purge queue. We have never used any > snapshots on this file system, so it definitely isn't about snapshots > holding data. Also, we increased the purge queue settings > (filer_max_purge_ops, mds_max_purge_* and friends) and definitely waited > long enough for all deletes to be processed (the objects were there > weeks after the file system was emptied). This was on a squid 19.2.3 > cluster. > In the tests that lead to this, both the file creation and deletions > were done in parallel using a few dozen clients - stressing the MDS for > sure. We had no crashes/problems on the cluster, we never had to do any > data recovery steps, i.e. the MDS appeared to work fine through the > tests. Also, this was a single MDS cluster, i.e. the problem isn't > related to subtrees moving across MDS's for example. The problem became > obvious since after removing all data from cephfs, we were expecting the > data pools to be empty, but they weren't. There were two pools, a > primary triple replicated one and an erasure coded one. Both of them > had stray objects. > > I didn't pursue this further since I wasn't sure what useful information > I could gather for a bug report - but it is certainly a curious > observation that perhaps large, long living cephfs clusters might have > significant space tied up in these objects that should have been removed > but weren't. Short of a full scan of all objects and matching them to > inodes - it is hard to tell how much even. > > Andras > > > On 7/2/26 12:17 PM, Andrej Filipčič via ceph-users wrote: > > > > So, to follow up on this, I did some further investigation. > > > > Checking for write amplification, I have copied 250TB of a mix of > > small and large files (20M of them), and the stored space on EC pool > > matched what was expected from actual data size to a few %. So EC > > overhead was not really a factor. Also, after the removal of this data > > set, the stored space was recovered as expected. > > > > The I checked the full dump of cephfs and compared it to list of all > > objects in the EC pool as follows: > > > > rados -p cephfs_data_echdd ls > echdd.objectlist > > > > find /ceph/ -printf "%i %p\n" > cephfs.inodes > > > > this took several hours, while in the meantime, writing and removing > > of data to cephfs was relatively low (few MB/s), so the impact of new > > objects and files should have been minimal. > > > > Then I selected all the objects of the form > > 1007b28abae.00000000 > > 100cce97f6d.00000000 > > 10067733861.00000000 > > 100cc4646aa.00000000 > > 200044d5c07.00000000 > > ... > > > > and checked if they match the files in the cephfs.inodes list > > > > ~3M of *.00000000 objects do not have the corresponding inode in the > > cephfs.inodes > > > > > > I did "rados stat" of ~70k of these objects (still running for all of > > them), and almost all have timestamps from March and April these year. > > On 4th of May I remember I have increased the mds purge queue values > > to speed up the removal of files since OSDs were filling up too > > quickly, and since then it seems the objects are not left uncleaned > > any more. > > > > With "rados getxattr objectid parent" I have checked several of them, > > and they all belong to two very active projects which typically write > > files with few GB/s all the time (and remove as well so space usage is > > not increasing). The objects I have checked belonged to files that > > were removed in cephfs, the projects have a separate file catalog > > which is consistent with cephfs contents. > > > > So, I do not understand why so many objects were left unremoved in EC > > pool in the period of 2 months, but at least, 3M uncleaned files > > explains 1.5PB of dark data by quick estimate. > > > > We also scrubbed cephfs root and ~mdsdir several times and no > > leftovers to remove were found. > > > > I hope the problem is gone now, but I would still like a good advice > > on how to proceed with the cleanup. I see these options: > > > > 1) remove the unmatched objects directly from EC pool with "rados > > rm". But this might have undesired side effects or corruption. > > > > 2) create a new EC pool and migrate all the data there by copying > > files in filesystem, and then destroy the old pool. > > > > 3) create a new filesystem with new EC pools and migrate the files. > > > > 4) run some advanced MDS disaster recovery procedure > > (cephfs-data-scan), but this requires offline FS and I do not want to > > recover old files from existing unmatched objects. Anyway, cephfs > > seems to be healthy now. > > > > Any good ideas? > > > > Best, > > Andrej > > > > > > On 10. 6. 2026 01:36, Anthony D'Atri via ceph-users wrote: > >>> ). > >>>>> There is ~5.6PiB stored on /ceph, shown by ceph.dir.rbytes with > >>>>> 132M files and 139M rentries. The pool shows 7PiB stored and > >>>>> 9.7PiB used consistent with 8+3 EC. > >>>>> The layout for most files: > >>>>> ceph.dir.layout="stripe_unit=16777216 stripe_count=1 > >>>>> object_size=16777216 pool=cephfs_data_echdd" > >>>>> > >>>>> But there is 1.4PiB discrepancy between the pool and the filesystem > >> Do you have scrubs enabled? Which if any non-default config options > >> do you have set? Any undersized or degraded or backfilling PGs? > >> > >> Which Ceph release? Do you have a sizable fraction of small files? > >> If you’re running Squid or earlier or don’t have EC optimizations > >> enabled, even a tiny file will allocate a multiple of 11*16=176 KB. > >> An 129KB file will consume 352KB, etc. If I understand those layout > >> options correctly. > >> > >> If that’s what’s going on, going to Tentacle with EC optimizations > >> would gain you some efficiency for files newly [re]written. You > >> could also migrate small files to a replicated pool. > >> > >> > >>>>> which I cannot explain and I suspect there are a lot of orphan > >>>>> objects there. I have run mds scrub on / and ~mdsdir as well. > >>>>> There is some mds damage on some old small files (~400 files), > >>>>> which I do not think it's relevant here. > >>>>> > >>>> Hello, > >>>> We had a similar issue last year with a group of users that created > >>>> and removed files at a very high rate. > >>>> > >>>> Have you read > >>>> > https://urldefense.com/v3/__https://docs.clyso.com/docs/kb/cephfs/*cephfs-pool-data-usage-growth-without-explanation__;Iw!!DSb-azq1wVFtOg!XcB7cJMEzAXsAddGg1LH5ff1B33dit2O1vAhxnVlv2MMUrC85oUKgukdaytYJQqAfmmjiTWJhr7GLPIKSTbwQpbx18c$ > >>>> ? > >>>> > >>>> We increased the purge rate parameters (very) aggressively to get > >>>> back to a comfortable situation (i.e. not a pool w/ near full > >>>> warnings). > >>>> > >>>> > >>>> Loïc. > >>> > >>> -- > >>> _____________________________________________________________ > >>> prof. dr. Andrej Filipcic, E-mail: [email protected] > >>> Department of Experimental High Energy Physics - F9 > >>> Jozef Stefan Institute, Jamova 39, P.o.Box 3000 > >>> SI-1001 Ljubljana, Slovenia > >>> Tel.: +386-1-477-3674 Fax: +386-1-477-3166 > >>> ------------------------------------------------------------- > >>> _______________________________________________ > >>> ceph-users mailing list -- [email protected] > >>> To unsubscribe send an email to [email protected] > >> _______________________________________________ > >> ceph-users mailing list -- [email protected] > >> To unsubscribe send an email to [email protected] > > > > > _______________________________________________ > ceph-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > _______________________________________________ ceph-users mailing list -- [email protected] To unsubscribe send an email to [email protected]
