From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: RAID10 - migrating disks without failing/degrading array? Date: Tue, 13 Oct 2009 18:20:36 -0400 Message-ID: <4AD4FD34.4090402@tmr.com> References: <72dbd3150910021122r474c43f6m2f1d953b5af9c3e0@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <72dbd3150910021122r474c43f6m2f1d953b5af9c3e0@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: David Rees Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids David Rees wrote: > I've got an 8 disk RAID10 array (near2 layout) where I am moving data > off some older disks onto newer disks. > > Currently what I'm doing is adding the newer disks as spares and then > failing/removing the older disks one at a time. > > This works fine, but leaves me with an hour or so of running the array > degraded while the spare drive syncs up which leaves me open for > data-loss during this time period. > > It seems like I should be able to add a drive as a directly > replacement for one of the drives I'm pulling out (so I temporarily > end up with 3-copies of that chunk instead of 2) until I pull > fail/remove the older disk. If I was using RAID0 striped over RAID1 > mirrors, for example, I know this is possible. > > Is this possible to do with RAID10? > In a slow, ugly, complex way, as someone described in another response. It involves using raid-1, and I suggest checking the write-mostly option as well, and involves some short time without the 2nd copy configured (and using check may not test everything on raid-10). Use a bitmap if you're not already. There is at least one other current thread regarding the need for a "clone member" feature in md, but unless someone with time and skills also has the problem, I doubt it's going to get added soon. -- Bill Davidsen Unintended results are the well-earned reward for incompetence.