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://docs.clyso.com/docs/kb/cephfs/#cephfs-pool-data-usage-growth-without-explanation
?
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]
--
_____________________________________________________________
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]
