From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 7 Jun 2000 18:08:03 +0200 From: "Andi Kleen" Subject: Re: [linux-lvm] LVM 0.8 and reiser filesystem Message-ID: <20000607180803.A26366@gruyere.muc.suse.de> References: <20000606184138.A8122@gruyere.muc.suse.de> <20000607140043.B5442@colombina.comedia.it> <20000607145954.A22712@gruyere.muc.suse.de> <20000607180455.Y3279@jadzia.josv.com> Mime-Version: 1.0 In-Reply-To: <20000607180455.Y3279@jadzia.josv.com>; from josv@osp.nl on Wed, Jun 07, 2000 at 06:04:55PM +0200 Sender: owner-linux-lvm Errors-To: owner-linux-lvm List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jos Visser Cc: Andi Kleen , linux-lvm@msede.com 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 :-) (The slowness of raidcheck is a big problem) -Andi