26 Mar
2020
26 Mar
'20
3:35 p.m.
Dear all, thanks for the hints. I was afraid I see ghosts.
Yes, we have quotas on many directories. I'm not entirely sure if there were different
quotas involved. I believe it was set only on the highest level, but now that you mention
it ...
I will try with quotas again, didn't include this in my scenario.
This information is really important, because it will affect how I as an admin can move
data between folders with quotas on them, which are typically used for sub-directory
mounts. For a user this would look like a magical move between file systems.
I will get back. Thanks!
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: Gregory Farnum <gfarnum(a)redhat.com>
Sent: 26 March 2020 15:20:51
To: Beocat KSU
Cc: ceph-users; Frank Schilder
Subject: Re: [ceph-users] Re: Move on cephfs not O(1)?
I was wondering that but at least in the userspace client the quotas
will just throw EXDEV or EDQUOT if it will exceed quotas...
...and EXDEV might trigger the kernel to do a copy-and-delete, I
guess? Not sure.
On Thu, Mar 26, 2020 at 7:18 AM Adam Tygart <mozes(a)ksu.edu> wrote:
Is there is a possibility that there was a quota involved? I've seen
moves between quota zones to cause a copy then delete.
--
Adam
On Thu, Mar 26, 2020 at 9:14 AM Gregory Farnum <gfarnum(a)redhat.com> wrote:
On Thu, Mar 26, 2020 at 5:49 AM Frank Schilder <frans(a)dtu.dk> wrote:
Some time ago I made a surprising observation. I reorganised a directory structure and
needed to move a folder one level up with a command like
mv A/B/ B
B contained something like 9TB in very large files. To my surprise, this command
didn't return for a couple of minutes and I started to look what was going on. What I
discovered was, that the mv command actually performed a full copy with a subsequent
remove. I had to wait for several hours for the move to complete.
I tried to reproduce this today to collect further information. However, this behaviour
seems not reproducible. No matter what I try, mv completes almost instantly.
I was running the original mv on mimic 13.2.2 and retried now with mimic 13.2.8. In
addition, there was an OS upgrade from Centos 7.6 to 7.7. I'm using the kernel-ml
versions (5.xxx). Only one cephfs mount was present at all times.
My questions are:
1) Was there a change from 13.2.2 to 13.2.8 explaining this?
No.
2) Are there (rare) conditions under which an mv
on cephfs becomes a cp+rm?
Not as part of CephFS.
3) Am I seeing ghosts?
The only way I can imagine this happening is if you had separate
CephFS mounts for cephfs/A/B and cephfs/ and you did the move between
them, instead of within the cephfs/ mount. :/
-Greg
Thanks for clues and best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
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