From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: Poor write performance with write-intent bitmap? Date: Wed, 22 Apr 2009 16:02:30 +0200 Message-ID: <87skk0947d.fsf@frosties.localdomain> References: <49ED096E.1000002@anonymous.org.uk> <49ED16F7.3040906@anonymous.org.uk> <4081b80da35818efbc07723240f8ea36.squirrel@neil.brown.name> <49ED2BC3.7050109@anonymous.org.uk> <87d4b5m4kf.fsf@frosties.localdomain> <49EF108D.4070605@anonymous.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <49EF108D.4070605@anonymous.org.uk> (John Robinson's message of "Wed, 22 Apr 2009 13:41:49 +0100") Sender: linux-raid-owner@vger.kernel.org To: John Robinson Cc: Goswin von Brederlow , Linux RAID List-Id: linux-raid.ids John Robinson writes: > On 22/04/2009 10:16, Goswin von Brederlow wrote: >> John Robinson writes: >>> Can't do that, my root filesystem is on the RAID-5, and part of the >>> reason for wanting the bitmap is because the md can't be stopped while >>> shutting down, so it was always wanting to resync at startup, which is >>> rather tedious. >> >> Normal shutdown should put the raid in read-only mode as last step. At >> least Debian does that. That way even a mounted raid will be clean >> after reboot. > > Yes, I would have thought it should as well. But I've just looked at > CentOS 5's /etc/rc.d/halt and as far as I can see it doesn't try to > switch md devices to read-only. Of course the root filesystem has gone > read-only but as we know that doesn't mean the device underneath it > gets told that. In particular we know that ext3 normally opens its > device read-write even when you're mounting the filesystem read-only > (iirc it's so it can replay the journal). > > Another issue might be the LVM layer; does that need to be stopped or > switched to read-only too? Debian does /sbin/vgchange -aln --ignorelockingfailure || return 2 before S60mdadm-raid, S60umountroot and S90reboot. >> I would also suggest restructuring your system like this: >> >> sdX1 1GB raid1 / (+/boot) >> sdX2 rest raid5 lvm with /usr, /var, /home, ... >> >> Both / and /usr can usualy be read-only preventing any filesystem >> corruption and raid resyncs in that part of the raid. > > I did do this multiple partition/LV thing once upon a time, but I got > fed up with having to resize things when one partition was full and > others empty. The machine is primarily a fileserver and Xen host, so > the dom0 only has 40GB of its own, and I couldn't be bothered > splitting that up. Having said all this, your suggestion is a good > one, it's just my preference to have it otherwise :-) > > Cheers, > > John. I've been using a 1GB / for years and years now so that won't be a problem. As for the rest one can also bind mount /usr, /var, /home to /mnt/space/* respectively. I.e. have just 2 (/ and everything else) partitions. Esspecially for XEN hosts I find LVM verry usefull. Makes it easy to create new logical volumes for new xen domains. MfG Goswin