From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 7 Jun 2000 18:23:03 +0200 From: Jos Visser Subject: Re: [linux-lvm] LVM 0.8 and reiser filesystem Message-ID: <20000607182303.A9261@jadzia.josv.com> References: <20000606184138.A8122@gruyere.muc.suse.de> <20000607140043.B5442@colombina.comedia.it> <20000607145954.A22712@gruyere.muc.suse.de> <20000607180455.Y3279@jadzia.josv.com> <20000607180803.A26366@gruyere.muc.suse.de> Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: <20000607180803.A26366@gruyere.muc.suse.de>; from ak@suse.de on Wed, Jun 07, 2000 at 06:08:03PM +0200 Sender: owner-linux-lvm Errors-To: owner-linux-lvm List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andi Kleen Cc: linux-lvm@msede.com 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? :-)