[linux-lvm] What is a good stripe size?
Heinz J. Mauelshagen
Mauelshagen at sistina.com
Fri Jun 22 14:25:01 UTC 2001
On Fri, Jun 22, 2001 at 10:49:21AM +0100, Joe Thornber wrote:
> On Fri, Jun 22, 2001 at 02:59:26AM +0200, Wolfgang Weisselberg wrote:
> > man pvmove:
> > [...]
> > You can move physical extents in use but make sure you
> > have an current backup in case of a system crash while
> > moving!!!
> > Now, this does *not* look like *crashproof*, does it?
> > This is from the CVS, btw, dated 2001-06-10.
> Do we update the metadata after each individual extent is moved ? Or
> at the end of the whole pvmove ?
Metadata is updated after every single moved extent.
The only reason why the man page says the above is the non atomic nature
of the metadata updates (2 block devices need to be updated; source and
destination) in case of the version 1 metadata layout.
With v2 (transaction oriented updates) we should be fine and can remove
the above warning.
> I'd assumed we were doing the former, in which case this comment from
> the man page is unduly pesimistic.
Yes, it is somehow pesimistic but disks can break, power can be
interupted or a million other things can happen which let the source device
metadata update make it but *not* the destination device update.
We could eventually recover from that situation by updating the destination
before the source and checking double entries for the same logical extent
on the source and destination device at VG activation time in order to remove
one of the two entries.
> - Joe
> linux-lvm mailing list
> linux-lvm at sistina.com
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
Mauelshagen at Sistina.com +49 2626 141200
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