From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Tripathy Subject: Re: possibly silly question (raid failover) Date: Wed, 02 Nov 2011 09:20:20 +0000 Message-ID: <4EB10B54.3010808@abpni.co.uk> 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> <20111102013756.GA10763@www5.open-std.org> <20111102124816.33a55447@notabene.brown> <20111102070221.GA24797@www5.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111102070221.GA24797@www5.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: keld@keldix.com Cc: NeilBrown , Miles Fidelman , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 02/11/2011 07:02, keld@keldix.com wrote: > On Wed, Nov 02, 2011 at 12:48:16PM +1100, NeilBrown wrote: >> On Wed, 2 Nov 2011 02:37:56 +0100 keld@keldix.com wrote: >> >>> 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 >> "just like raid1+0" > No, that is not the case AFAIK. Eg the layout of raid10,f2 with 4 disks is > "just like raid0+1". > Isn't md raid10 n2 exactly the same as RAID1+0??