Alexander,
Thanks for explaining this. As I suspected, this is a high abstract
pursuit of what caused the problem, and while I'm sure this makes sense
for Ceph developers, it isn't going to happen in this case.
I don't care how it got this way- the tools used to create this pool
will never be used in our environment again after I recover this disk
space - the entire reason I need to recover the missing space is so I
can move enough filesystems around to remove the current structure and
the tools that made it.
I only need to get that disk space back. Any analysis I do will be
solely directed towards achieving that.
Thanks.
On 21/03/2024 3:10 am, Alexander E. Patrakov wrote:
Hi Thorne,
The idea is quite simple. By retesting the leak with a separate pool,
used by nobody except you, in the case if the leak exists and is
reproducible (which is not a given), you can definitely pinpoint it
without giving any chance to the alternate hypothesis "somebody wrote
some data in parallel". And then, even if the leak is small but
reproducible, one can say that multiple such events accumulated to 10
TB of garbage in the original pool.
On Wed, Mar 20, 2024 at 7:29 PM Thorne Lawler <thorne@xxxxxxxxxxx> wrote:
Alexander,
I'm happy to create a new pool if it will help, but I don't
presently see how creating a new pool will help us to identify the
source of the 10TB discrepancy in this original cephfs pool.
Please help me to understand what you are hoping to find...?
On 20/03/2024 6:35 pm, Alexander E. Patrakov wrote:
Thorne,
That's why I asked you to create a separate pool. All writes go
to the original pool, and it is possible to see object counts
per-pool.
On Wed, Mar 20, 2024 at 6:32 AM Thorne Lawler
<thorne@xxxxxxxxxxx> wrote:
Alexander,
Thank you, but as I said to Igor: The 5.5TB of files on this
filesystem are virtual machine disks. They are under
constant, heavy write load. There is no way to turn this off.
On 19/03/2024 9:36 pm, Alexander E. Patrakov wrote:
Hello Thorne,
Here is one more suggestion on how to debug this. Right now, there is
uncertainty on whether there is really a disk space leak or if
something simply wrote new data during the test.
If you have at least three OSDs you can reassign, please set their
CRUSH device class to something different than before. E.g., "test".
Then, create a new pool that targets this device class and add it to
CephFS. Then, create an empty directory on CephFS and assign this pool
to it using setfattr. Finally, try reproducing the issue using only
files in this directory. This way, you will be sure that nobody else
is writing any data to the new pool.
On Tue, Mar 19, 2024 at 5:40 PM Igor Fedotov<igor.fedotov@xxxxxxxx> <mailto:igor.fedotov@xxxxxxxx> wrote:
Hi Thorn,
given the amount of files at CephFS volume I presume you don't have
severe write load against it. Is that correct?
If so we can assume that the numbers you're sharing are mostly refer to
your experiment. At peak I can see bytes_used increase = 629,461,893,120
bytes (45978612027392 - 45349150134272). With replica factor = 3 this
roughly matches your written data (200GB I presume?).
More interestingly is that after file's removal we can see 419,450,880
bytes delta (=45349569585152 - 45349150134272). I could see two options
(apart that someone else wrote additional stuff to CephFS during the
experiment) to explain this:
1. File removal wasn't completed at the last probe half an hour after
file's removal. Did you see stale object counter when making that probe?
2. Some space is leaking. If that's the case this could be a reason for
your issue if huge(?) files at CephFS are created/removed periodically.
So if we're certain that the leak really occurred (and option 1. above
isn't the case) it makes sense to run more experiments with
writing/removing a bunch of huge files to the volume to confirm space
leakage.
On 3/18/2024 3:12 AM, Thorne Lawler wrote:
Thanks Igor,
I have tried that, and the number of objects and bytes_used took a
long time to drop, but they seem to have dropped back to almost the
original level:
* Before creating the file:
o 3885835 objects
o 45349150134272 bytes_used
* After creating the file:
o 3931663 objects
o 45924147249152 bytes_used
* Immediately after deleting the file:
o 3935995 objects
o 45978612027392 bytes_used
* Half an hour after deleting the file:
o 3886013 objects
o 45349569585152 bytes_used
Unfortunately, this is all production infrastructure, so there is
always other activity taking place.
What tools are there to visually inspect the object map and see how it
relates to the filesystem?
Not sure if there is anything like that at CephFS level but you can use
rados tool to view objects in cephfs data pool and try to build some
mapping between them and CephFS file list. Could be a bit tricky though.
On 15/03/2024 7:18 pm, Igor Fedotov wrote:
ceph df detail --format json-pretty
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Standard ITGOV40172
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Alexander E. Patrakov
--
Regards,
Thorne Lawler - Senior System Administrator
*DDNS* | ABN 76 088 607 265
First registrar certified ISO 27001-2013 Data Security Standard
ITGOV40172
P +61 499 449 170
_DDNS
/_*Please note:* The information contained in this email message
and any attached files may be confidential information, and may
also be the subject of legal professional privilege. _If you are
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email is unauthorised. _If you received this email in error,
please notify Discount Domain Name Services Pty Ltd on 03 9815
6868 to report this matter and delete all copies of this
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Alexander E. Patrakov
--
Regards,
Thorne Lawler - Senior System Administrator
*DDNS* | ABN 76 088 607 265
First registrar certified ISO 27001-2013 Data Security Standard ITGOV40172
P +61 499 449 170
_DDNS
/_*Please note:* The information contained in this email message and any
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