From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Evans Subject: Re: 3 disk RAID1? Date: Mon, 8 Mar 2010 14:11:10 -0800 Message-ID: <4877c76c1003081411p3c729c89q3d908d07f19b0857@mail.gmail.com> References: <5bdc1c8b1003081239l32c5653fs8347179e23c0a287@mail.gmail.com> <20100308205803.GA31731@cthulhu.home.robinhill.me.uk> <5bdc1c8b1003081304n7a59e99ej1f66078090980f06@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <5bdc1c8b1003081304n7a59e99ej1f66078090980f06@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Mark Knecht Cc: Linux-RAID List-Id: linux-raid.ids On Mon, Mar 8, 2010 at 1:04 PM, Mark Knecht wrot= e: > On Mon, Mar 8, 2010 at 12:58 PM, Robin Hill w= rote: >> On Mon Mar 08, 2010 at 12:39:26PM -0800, Mark Knecht wrote: >> >>> Hi all, >>> =A0 =A0I'm still very much on a steep learning curve about what I c= an do >>> with Linux software RAID. In another thread this weekend a couple o= f >>> responders discussed among themselves 3-disk RAID1 solutions that c= an >>> survive if 2 disks die. I don't understand what that means. Can >>> someone point me at a quick explanation? Is that really possible? >>> >>> =A0 =A0In general I'm using a few Wikipedia pages and gravitate tow= ard 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) >>> >>> =A0 =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 tw= o >>> 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. =A0And RAID only pro= tects >> against hardware failures, so you know which disk has failed because= it >> gets kicked out of the array as faulty. =A0This is the same regardle= ss 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 bloc= k 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 softwa= re >> RAID - if not, please specify what you're intending to use). =A0The = manual >> page for mdadm should give you everything you need - do ask if there= 's >> anything you want clarifying though. >> >> Cheers, >> =A0 =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"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at =A0http://vger.kernel.org/majordomo-info.html > When in doubt, read the manual two or three more times. This might also help you: http://wiki.tldp.org/LVM-on-RAID I wrote some background comparison sections when I made that... -- 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