qm: guest trim: add note mentioning issue with ext4

It is rather unexpected and seems worth mentioning. Reported in the
community forum [0] and the explanation found by Alwin [1].

[0]: https://forum.proxmox.com/threads/123819/
[1]: https://serverfault.com/questions/1113127/fstrim-is-very-slow-on-xfs-and-always-return-same-value-unlike-ext4/1113129#1113129

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
This commit is contained in:
Fiona Ebner 2023-03-10 10:06:48 +01:00 committed by Thomas Lamprecht
parent be609f0589
commit 95117b6cdf

View File

@ -1063,6 +1063,12 @@ operations that have the potential to write out zeros to the storage:
On a thin provisioned storage, this can help to free up unused space.
NOTE: There is a caveat with ext4 on Linux, because it uses an in-memory
optimization to avoid issuing duplicate TRIM requests. Since the guest doesn't
know about the change in the underlying storage, only the first guest-trim will
run as expected. Subsequent ones, until the next reboot, will only consider
parts of the filesystem that changed since then.
Troubleshooting
^^^^^^^^^^^^^^^