From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: [BUG] non-metadata arrays cannot use more than 27 component devices Date: Sat, 25 Feb 2017 17:00:58 -0500 Message-ID: References: <20170224040816.41f2f372.ian_bruce@mail.ru> <41ea334c-ae1c-dac6-e1a1-480d3700a588@turmel.org> <20170224084024.4dfe83a2.ian_bruce@mail.ru> <1e40da0d-b175-9ff5-d2e5-cf1f25aacc26@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Anthony Youngman , ian_bruce@mail.ru, linux-raid@vger.kernel.org List-Id: linux-raid.ids On 02/25/2017 03:05 PM, Anthony Youngman wrote: > Although I would have thought build mode was superb for doing > backups without needing to stop using the system ... I haven't seen > any documentation about things like breaking raid to do backups and > all that sort of thing. > > I need to investigate it, but I'd like to know how to suspend a > mirror, back it up, and then resume. The databases I work with have > an option that suspends all new writes, but flushes all current > transactions to disk so the disk is consistent for backing up. So if > you do that and back up the database you know your backup is > consistent. > > This is all a rather important usage of raid, actually, imho. It > seems so obvious - create a temporary mirror, wait for the sync to > complete, suspend i/o to get the disk consistent, then you can break > the mirror and carry on. Terabytes :-) of data safely backed up in > the space of seconds. No. Don't go there. There's already a technology out there that does this correctly, called LVM snapshots. And they let you resume normal operations after a very brief hesitation, and the snapshot holds the static image while you copy it off. Phil