From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Knecht Subject: Re: 3 disk RAID1? Date: Mon, 8 Mar 2010 13:04:37 -0800 Message-ID: <5bdc1c8b1003081304n7a59e99ej1f66078090980f06@mail.gmail.com> References: <5bdc1c8b1003081239l32c5653fs8347179e23c0a287@mail.gmail.com> <20100308205803.GA31731@cthulhu.home.robinhill.me.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20100308205803.GA31731@cthulhu.home.robinhill.me.uk> Sender: linux-raid-owner@vger.kernel.org To: Linux-RAID List-Id: linux-raid.ids On Mon, Mar 8, 2010 at 12:58 PM, Robin Hill wro= te: > On Mon Mar 08, 2010 at 12:39:26PM -0800, Mark Knecht wrote: > >> Hi all, >> =C2=A0 =C2=A0I'm still very much on a steep learning curve about wha= t I can do >> with Linux software RAID. In another thread this weekend a couple of >> responders discussed among themselves 3-disk RAID1 solutions that ca= n >> survive if 2 disks die. I don't understand what that means. Can >> someone point me at a quick explanation? Is that really possible? >> >> =C2=A0 =C2=A0In general I'm using a few Wikipedia pages and gravitat= e toward the >> diagrams as much as anything. >> >> http://en.wikipedia.org/wiki/RAID >> http://en.wikipedia.org/wiki/RAID1#RAID_1 >> >> RAID0 - striping, speed not reliability (2 disk minimum) >> RAID1 - duplicate data, no other protection (2 disk minimum) >> >> =C2=A0 =C2=A0How do I build RAID1 using three drives? Just duplicate= the data 3 >> times? If drives start going bad how do I determine which one or two >> are failing? (fsck? SMART?) With 3 drives 1 fail seems relatively >> straightforward to figure out, but 2? >> > A 3-disk RAID1 is just 3 duplicate copies, yes. =C2=A0And RAID only p= rotects > against hardware failures, so you know which disk has failed because = it > gets kicked out of the array as faulty. =C2=A0This is the same regard= less of > how many mirrored copies you have (md will detect a write failure to = a > drive and mark it as faulty - read errors will cause the failed block= to > get rewritten). > > As for how to create it - it's just the same process as for a 2-disk > RAID1 but specifying 3 drives (assuming you're using Linux md softwar= e > RAID - if not, please specify what you're intending to use). =C2=A0Th= e manual > page for mdadm should give you everything you need - do ask if there'= s > anything you want clarifying though. > > Cheers, > =C2=A0 =C2=A0Robin Thanks Robin. Maybe I am getting smarter about this if I'm figuring out what others are talking about! ;-) Cheers, Mark -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html