On Mon, 23 Sep 2024, Steve Keller wrote:
Tim Woodall <debianu...@woodall.me.uk> writes:
The raid rebuild is a particular pain point IMO. It's important to do a
discard after a failed disk rebuild otherwise every block is 'in use' on
the underlying storage.
Hmm, does a RAID rebuild really always copy the whole new disk, even
the unused space? But what kind of info is then kept in the first
128 MiB of /dev/md0, if not a flag for every block telling whether it's
used or not?
After a rebuild I always create a LV with all the free space and then
discard it.
:(
I currently have RAID only on a server with HDDs which don't support
TRIM anyway. I have only needed twice to rebuild the RAID-1 with 2
disks and I seem to remember that not the whole disk was copied, but I
might be wrong on that.
I think the bitmaps are for dirty blocks - so a resynch after a power
failure is quick, not for a failed disk replacement rebuild.
But perhaps there's a config option somewhere so that the md device can
track discards in a bitmap.
My guess is most people run at 90% capacity so it's not that useful...
