From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Youngman Subject: Re: linux raid wiki - backup files Date: Mon, 21 Nov 2016 20:22:09 +0000 Message-ID: References: <583077D0.5070804@youngman.org.uk> <5831B7B9.8090008@youngman.org.uk> <4febebb6-0442-cc5e-45d5-e041e21e2d95@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4febebb6-0442-cc5e-45d5-e041e21e2d95@turmel.org> Sender: linux-raid-owner@vger.kernel.org To: Phil Turmel , linux-raid , neilb@suse.com List-Id: linux-raid.ids On 21/11/16 14:07, Phil Turmel wrote: > On 11/20/2016 09:48 AM, Wols Lists wrote: >> On 20/11/16 00:27, Phil Turmel wrote: >>> Yes. But the new stripes lay on top of the old stripes, unless you move >>> the data offset. Which is why a backup file holds the old stripe just >>> in case. If you can move the offset, you use the lower offset for the >>> lower addresses in the array, and the higher offset for the higher >>> addresses, on either side of the reshape position. >> >> Okay, understood. So v0.9 and v1.0 always need a backup for a reshape. Having looked at the man page, this now seems obvious - the superblock is at the end, so the data offset is 0. But for a 1.0 array, could we create a data offset? (So, if we created a data offset, we could then move the superblock and convert a 1.0 to 1.1 or 1.2? Okay, it can't do it now, but it looks to me like it shouldn't be that hard ... ?) >> >> But if we have a data offset with v1.2, a reshape will use that space if >> it can rather than needing a backup file? > I'm guessing that 1.0 and 1.1 defaulted to no data offset to speak of? And if we (can) create a decent data offset, we can then use that in exactly the same way as with v1.2? Cheers, Wol