From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: Adding a bitmap, v 0.90 superblocks Date: Fri, 1 Aug 2008 13:11:07 +1000 Message-ID: <18578.32459.608646.540653@notabene.brown> References: <20080729184416.GA7655@nexus.edgeofthenet.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Richard Michael on Tuesday July 29 Sender: linux-raid-owner@vger.kernel.org To: Richard Michael Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Tuesday July 29, rmichael-raid@edgeofthenet.org wrote: > I would like to add an internal bitmap to my RAID1 array. It uses > v 0.90 superblocks. > > Reading the man page, I believe I do this with: > > "mdadm --grow --bitmap=internal /dev/mdX" > > correct? Correct! > > How do I know how much space is available on the superblock when mdadm > will perform it's computation "to make best use of available space"? > I'm curious because perhaps I should change to 1.x superblocks in the > future (for non-bootable arrays). with 0.90, there is about 60K guaranteed to be available. This is 491520 bits. With 1.0 there 3K guaranteed to be available, though there might be more. I don't think we use the "more" currently unless you add a bitmap when creating the array. So there is no need to change metadata version for more bitmap space. NeilBrown