From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: How to initialize "composite" RAID Date: Sat, 11 Sep 2010 15:09:23 +1000 Message-ID: <20100911150923.41043519@notabene> References: <20100910222814.CB50615242D@gemini.denx.de> <20100911083748.14843721@notabene> <20100911090709.580f3539@notabene> <20100911102319.2435d878@notabene> <20100911144226.59ebc03d@notabene> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mike Hartman Cc: Wolfgang Denk , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Sat, 11 Sep 2010 00:58:21 -0400 Mike Hartman wrote: > > If you add a bitmap (mdadm --grow /dev/md0 --bitmap=internal) after the > > current resync finished, then any subsequent resync due to an unclean > > shutdown will be much faster. > > I read somewhere (I think in the wiki) that an intent bitmap only > works properly on ext2 and ext3 and can cause trouble on other file > systems. Can I use one on ext4 (what I'm using)? I'm hoping/assuming > what I read just predates the common use of ext4. That is completely wrong. An intent bitmap works properly no matter what filesystem is on top. It does impose a small performance penalty for writes which is very work-load-dependant, and it is not impossible that different filesystems would suffer more or less from this, but I doubt you would notice. If you can find it again let me know and I'll try to get it fixed. > > Will I need to remove the bitmap before adding another disk and > growing the array to use it? If I don't, will it speed up that > operation any? You, you will need to remove the bitmap before growing the array. I really should fix that but it doesn't seem to rise to the top of my to-do list... And no, a bitmap would have no effect on a reshape operation even if it were allowed to be present. NeilBrown