Am 07.11.2022 16:29, schrieb hede:
Am 07.11.2022 02:57, schrieb hw:
Hi,
Is there no VDO in Debian, and what would be good to use for
deduplication with
Debian? Why isn't VDO in the stardard kernel? Or is it?
I have used vdo in Debian some time ago and didn't remember big
problems.
Btw. please keep in mind: VDO is transparent to the filesystem on-top.
And deduplication (likewise compression) is some non-deterministic task.
Where btrfs' calculation of the real free space is tricky if compression
and/or dedup is in use, it's quite impossible for a filesystem ontop of
VDO. It's much wore with VDO. The filesystem on top sees a "virtual"
size of the device which is a vague guess at best and is predefined on
creation time. You need to carefully monitor the actual disk usage of
the VDO device and stop writing data to the filesystem if it fills up.
It stalls if the filesystem wants to write more data than is available.
(At least if I remember correctly. Please correct me if I'm wrong here.)
So if you are expecting issues with space, there's some risk in damaging
your (file-)system.
With something like btrfs or ZFS there's less risk in that. Both do know
the free space and even if this was indeed a Problem in first days*,
rebalancing and filled up filesystems are (AFAIK) no longer a problem
with btrfs.
*) running out of space on btrfs could render filesystems read-only,
deleting files was no longer possible. COW means even deleting a file
needs some space so it got broken. This is AFAIK resolved. For deleting
files there's always some reserved space.
regards
hede
