From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miles Fidelman Subject: Re: wish for Linux MD mirrored raid types Date: Fri, 06 May 2011 12:23:12 -0400 Message-ID: <4DC42070.2070401@meetinghouse.net> References: <20110506071752.GA22063@www2.open-std.org> <20110506133159.30c66519@natsu> <20110506090345.GA22245@www2.open-std.org> <4DC3BDD9.1060300@abpni.co.uk> <20110506094102.GC22245@www2.open-std.org> <20110506155059.6f82cbeb@natsu> <4DC3C804.6080200@abpni.co.uk> <20110506132739.GA22689@www2.open-std.org> <4DC3FF4C.5090502@meetinghouse.net> <20110506152405.GB22964@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Roberto Spadim wrote: > hum, i asked this question one time, the point is: > raid1 code is very easy > raid10 code is more complex > > easy =3D faster, less memory, less cpu > complex =3D faster?, more memory? more cpu? > > check others raid system (freebsd, netbsd) and check how they do... > > 2011/5/6 Keld J=F8rn Simonsen: > =20 >>> Keld J=F8rn Simonsen wrote: >>> =20 >>>>> As you say, RAID10,near on four disks is pretty much identical to >>>>> RAID1+0 - i.e., a stripe of two normal RAID1 pairs. >>>>> >>>>> =20 of course RAID10 offers the far option, and the option to run on an odd= =20 number of drives (I currently use it on a couple of 4-drive servers, bu= t=20 as I look at some replacement hardware I've been thinking that RAID10=20 on a 5-drive configuration offers a nice mix of reliability and perform= ance) re. easy/complex - I'm not sure I really believe that - when I've=20 reviewed options, I come to the conclusion that: RAID1 - wastes a lot of drive space, particularly if you want to=20 maintain reliability after a single-drive failure (requires a minimum o= f=20 3 mirrored drives) RAID5 and RAID6 are better when it comes to mixing efficiency with=20 multi-drive failures, but have a couple of odd failure modes and are a=20 real pain to rebuild after a failure RAID1+0 and RAID0+1 are interesting combination - but my sense is that=20 every time you nest a layer, you're adding configuration complexity,=20 processing delays (low level cpu cycles and i/o transactions), and just= =20 that much more complexity if you have to reconfigure or rebuild and=20 array (particularly if you're running LVM and DRBD on top of the basic=20 disk arrays, as I am) md RAID10 chops out a layer of nesting and makes better use of disk=20 space - by combining block replication and striping into a single layer= =20 - providing what, to me, is a good balance of disk use, multiple copies= =20 of data, performance, and managability - so far, its worked well for me --=20 In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra -- 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