[pve-devel] [PATCH docs] qm: guest trim: add note mentioning issue with ext4
f.ebner at proxmox.com
Fri Mar 10 10:06:48 CET 2023
It is rather unexpected and seems worth mentioning. Reported in the
community forum  and the explanation found by Alwin .
Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
qm.adoc | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/qm.adoc b/qm.adoc
index bd535a2..3ba2a3c 100644
@@ -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.
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