[linux-lvm] LVM commands extremely slow during raid check/resync

[Larkin Lowrey]

That helped bring the lvcreate time down from 2min to 1min so that's an
improvement.  Thank you.

The source of the remaining slowdown is the writing of metadata to my 4
PVs. The writes are small and the arrays are all raid5 so each metadata
write is also requiring a read. I'm still at a loss for why this was not
a problem when running F15 but the filter is a workable solution for me
so I'll leave it alone.

--Larkin

On 3/26/2012 3:55 PM, Ray Morris wrote:
> Put -vvvv on the command and see what takes so long. In our case, 
> it was checking all of the devices to see if they were PVs.
> "All devices" includes LVs, so it was checking LVs to see if they
> were PVs, and activating an LV triggered a scan in case it was 
> a PV, so activating a volume group was especially slow (hours).
> The solution was to use "filter" in lvm.conf like this:
>
> filter = [ "r|^/dev/dm.*|", "r|^/dev/vg-.*|","a|^/dev/sd*|", "a|^/dev/md*|", "r|.*|" ]
>
> That checks only /dev/sd* and /dev/md*, to see if they are PVs, 
> skipping the checks of LVs to see if they are also PVs. Since the
> device list is cached, use vgscan -vvvv to check that it's checking 
> the right things and maybe delete that cache first. My rule IS 
> a bit redundant because I had trouble getting the simpler form 
> to do what I wanted. I ended up using a belt and suspenders 
> approach, specifying both "do not scan my LVs" and "scan only
> /dev/sd*".