[linux-lvm] LVM 0.8 and reiser filesystem
Jos Visser
josv at osp.nl
Wed Jun 7 16:23:03 UTC 2000
And thus it came to pass that Andi Kleen wrote:
(on Wed, Jun 07, 2000 at 06:08:03PM +0200 to be exact)
> On Wed, Jun 07, 2000 at 06:04:55PM +0200, Jos Visser wrote:
> > The way HP's logical volume manager does it is by maintaining a kind of
> > data log somewhere in the volume metadata. This log (let's call it the
> > Mirror Write Cache) is effectively a bitmap which keeps track of which
> > blocks in the logical volume are hit by a write. The unit of
> > granularity here is not an individual block, but something that is
> > called a Large Track Group (LTG, let's say a couple of MB). Whenever
> > all parallel writes are finished, the corresponding LTG bit in the MWC
> > is cleared and the MWC on disk is (eventually) updated.
> >
> > After a crash when the Volume Group is activated, all copies (plexes)
> > of a volume must be synchronized. The VM software inspects the MWC, and
> > then knows which blocks might be out of sync across the plexes. Only
> > these blocks are then synchronized using a read from the preferred plex
> > and write to all other plexes. The MWC is used to prevent a full sync
> > after a crash.
>
> Sounds clever. I really wish Linux raid would use this optimization :-)
Well, the source is there, unfortunately I've got something to do tonight :-)
++Jos
> (The slowness of raidcheck is a big problem)
>
> -Andi
--
The InSANE quiz master is always right!
(or was it the other way round? :-)
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