From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: Strange RAID-5 rebuild problem Date: Mon, 3 Mar 2008 11:33:36 +1100 Message-ID: <18379.18272.464486.925011@notabene.brown> References: <656D8E57-804D-4A63-B9CA-D3C899616F61@it-loops.com> <3816592D-B75C-4B00-B3B7-65AE3B403DB0@it-loops.com> <20080301222326.GA20435@cthulhu.home.robinhill.me.uk> <2BABB51E-7701-44D4-AD07-6394CCF77941@it-loops.com> <244F7F54-081B-462E-A0AD-8E5E1056B90B@it-loops.com> <47CA7CE0.9050702@msgid.tls.msk.ru> <0D90EC1B-DE2A-4A9B-A63C-323838FF937A@it-loops.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Michael Guntsche on Sunday March 2 Sender: linux-raid-owner@vger.kernel.org To: Michael Guntsche Cc: Michael Tokarev , linux-raid@vger.kernel.org, Robin Hill List-Id: linux-raid.ids On Sunday March 2, mike@it-loops.com wrote: > > So apparently it does switch to read-write on the first write > request, but the rebuild is not continuing. Yes. This bug is fixed by the following patch which I have just sent of for inclusion in mainline. The patches talks about "reshape" but it applies to "resync" too. The workaround is to "mdadm -w" before the first write. Thanks, NeilBrown Make sure a reshape is started when device switches to read-write. A resync/reshape/recovery thread will refuse to progress when the array is marked read-only. So whenever it mark it not read-only, it is important to wake up thread resync thread. There is one place we didn't do this. The problem manifests if the start_ro module parameters is set, and a raid5 array that is in the middle of a reshape (restripe) is started. The array will initially be semi-read-only (meaning it acts like it is readonly until the first write). So the reshape will not proceed. On the first write, the array will become read-write, but the reshape will not be started, and there is no event which will ever restart that thread. Signed-off-by: Neil Brown ### Diffstat output ./drivers/md/md.c | 1 + 1 file changed, 1 insertion(+) diff .prev/drivers/md/md.c ./drivers/md/md.c --- .prev/drivers/md/md.c 2008-02-22 15:46:25.000000000 +1100 +++ ./drivers/md/md.c 2008-02-22 15:46:52.000000000 +1100 @@ -5356,6 +5356,7 @@ void md_write_start(mddev_t *mddev, stru mddev->ro = 0; set_bit(MD_RECOVERY_NEEDED, &mddev->recovery); md_wakeup_thread(mddev->thread); + md_wakeup_thread(mddev->sync_thread); } atomic_inc(&mddev->writes_pending); if (mddev->in_sync) {