From mboxrd@z Thu Jan 1 00:00:00 1970 From: keld@keldix.com Subject: Re: possibly silly question (raid failover) Date: Wed, 2 Nov 2011 02:37:56 +0100 Message-ID: <20111102013756.GA10763@www5.open-std.org> References: <4EAF3F78.5060900@meetinghouse.net> <4EAFEE95.6070608@meetinghouse.net> <4EAFF636.6060904@anonymous.org.uk> <4EB052E6.4050400@meetinghouse.net> <20111101221539.GA1319@www5.open-std.org> <20111102092526.50b410b1@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20111102092526.50b410b1@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Miles Fidelman , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, Nov 02, 2011 at 09:25:26AM +1100, NeilBrown wrote: > On Tue, 1 Nov 2011 23:15:39 +0100 keld@keldix.com wrote: > > > On Tue, Nov 01, 2011 at 04:13:26PM -0400, Miles Fidelman wrote: > > > David Brown wrote: > > > > > > > >No, md RAID10 does /not/ offer more redundancy than RAID1. You are > > > >right that md RAID10 offers more than RAID1 (or traditional RAID0 over > > > >RAID1 sets) - but it is a convenience and performance benefit, not a > > > >redundancy benefit. In particular, it lets you build RAID10 from any > > > >number of disks, not just two. And it lets you stripe over all disks, > > > >improving performance for some loads (though not /all/ loads - if you > > > >have lots of concurrent small reads, you may be faster using plain > > > >RAID1). > > > > In fact raid10 mas a bit less redundancy than raid1+0. > > It is as far as I know built as raid0+1 with a disk layout > > where you can only loose eg 1 out of 4 disks, while raid1+0 > > in some cases can loose 2 disks out of 4. > > With md/raid10 you can in some case lose 2 out of 4 disks and survive, just > like raid1+0. OK, in which cases, and when is this not the case? best regards keld