Hi Steve, On Thu, 12 Mar 2026 at 19:16, Steve Yates <steve@teamits.com> wrote:
Hi Alwin,
All VM disks are set as SSD with discard enabled.
“Run guest-trim after a disk move or VM migration” was not checked. I didn’t realize that was in there! I don’t think that applies though? Per https://pve.proxmox.com/pve-docs/chapter-qm.html#qm_qemu_agent :
“With this enabled, Proxmox VE will issue a trim command to the guest after the following operations that have the potential to write out zeros to the storage:
- moving a disk to another storage - live migrating a VM to another node with local storage”
…and using Ceph the disk doesn’t move if we migrate a VM…? Plus trim is being run weekly. Maybe I could stop a VM and move its disk to local storage and back into Ceph again but that would take quite a lot of time and seems like little to no gain except maybe a lower object count.
That's what I meant as an alternative.
That section also has this note on ext4, matching previous discussions: “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.”
Exactly that. Even if the in-memory bitmap disappears, the underlying misalignment issue will remain and affect any guest. Cheers, Alwin