Hi John,
I am running ceph Luminous 12.2.1 release on the storage nodes with v4.4.114 kernel on the cephfs clients.
3 client nodes are running 3 instances of a test program.
The test program is doing this repeatedly in a loop:
- sequentially write a 256GB file on cephfs
- delete the file
‘ceph df’ shows that after delete the space is not getting freed from cephfs and and cephfs space utilization (number of objects, space used and % utilization) keeps growing up continuously.
I double checked, and no process is holding an open handle to the closed files.
When the test program is stopped, the writing workload stops and then the cephfs space utilization starts going down as expected.
Looks like the cephfs write load is not giving enough opportunity to actually perform the delete file operations from clients. It is a consistent behavior, and easy to reproduce.
I tried playing with these advanced MDS config parameters:
- mds_max_purge_files
- mds_max_purge_ops
- mds_max_purge_ops_per_pg
- mds_purge_queue_busy_flush_period
But it is not helping with the workload.
Is this a known issue? And is there a workaround to give more priority to the objects purging operations?
Thanks in advance,
Nitin
From: ceph-users <ceph-users-bounces@xxxxxxxxxxxxxx> on behalf of Alexander Ryabov <aryabov@xxxxxxxxxxxxxx>
Date: Thursday, July 19, 2018 at 8:09 AM
To: John Spray <jspray@xxxxxxxxxx>
Cc: "ceph-users@xxxxxxxxxxxxxx" <ceph-users@xxxxxxxxxxxxxx>
Subject: Re: Force cephfs delayed deletion
>Also, since I see this is a log directory, check that you don't have some processes that are holding their log files open even after they're unlinked.
Thank you very much - that was the case.
lsof /mnt/logs | grep deleted
After dealing with these, space was reclaimed in about 2-3min.
From: John Spray <jspray@xxxxxxxxxx>
Sent: Thursday, July 19, 2018 17:24
To: Alexander Ryabov
Cc: ceph-users@xxxxxxxxxxxxxx
Subject: Re: Force cephfs delayed deletion
On Thu, Jul 19, 2018 at 1:58 PM Alexander Ryabov <aryabov@xxxxxxxxxxxxxx> wrote:
Hello,
I see that free space is not released after files are removed on CephFS.
I'm using Luminous with replica=3 without any snapshots etc and with default settings.
From client side:
$ du -sh /mnt/logs/
4.1G /mnt/logs/
$ df -h /mnt/logs/
Filesystem Size Used Avail Use% Mounted on
h1,h2:/logs 125G 87G 39G 70% /mnt/logs
These stats are after couple of large files were removed in /mnt/logs dir, but that only dropped Useв space a little.
Check what version of the client you're using -- some older clients had bugs that would hold references to deleted files and prevent them from being purged. If you find that the space starts getting freed when you unmount the client, this is likely to be because of a client bug.
Also, since I see this is a log directory, check that you don't have some processes that are holding their log files open even after they're unlinked.
John
Doing 'sync' command also changes nothing.
From server side:
# ceph df
GLOBAL:
SIZE AVAIL RAW USED %RAW USED
124G 39226M 88723M 69.34
POOLS:
NAME ID USED %USED MAX AVAIL OBJECTS
cephfs_data 1 28804M 76.80 8703M 7256
cephfs_metadata 2 236M 2.65 8703M 101
Why there are such a large difference between 'du' and 'USED'?
I've found that it could be due to 'delayed delete' http://docs.ceph.com/docs/luminous/dev/delayed-delete/
And previously it seems could be tuned by adjusting the "mds max purge files" and "mds max purge ops"
http://lists.ceph.com/pipermail/ceph-users-ceph.com/2016-October/013679.html
But there is no more of such options in http://docs.ceph.com/docs/luminous/cephfs/mds-config-ref/
So the question is - how to purge deleted data and reclaim free space?
Thank you.
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