From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miles Fidelman Subject: Re: possibly silly question (raid failover) Date: Tue, 01 Nov 2011 17:32:17 -0400 Message-ID: <4EB06561.8090706@meetinghouse.net> References: <4EAF3F78.5060900@meetinghouse.net> <4EAFEE95.6070608@meetinghouse.net> <4EAFF636.6060904@anonymous.org.uk> <4EB052E6.4050400@meetinghouse.net> <20111101212023.GA20565@cthulhu.home.robinhill.me.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111101212023.GA20565@cthulhu.home.robinhill.me.uk> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Robin Hill wrote: > On Tue Nov 01, 2011 at 04:13:26 -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). >> wasn't suggesting that it does - just that it does things differently >> than normal raid 1+0 - for example, by doing mirroring and striping as a >> unitary operation, it works across odd number of drives - it also (I >> think) allows for more than 2 copies of a block (not completely clear >> how many copies of a block would be made if you specified a 16 drive >> array) - sort of what I'm wondering here >> > By default it'll make 2 copies, regardless how many devices are in the > array. You can specify how many copies you want though, so -n3 will give > you a near configuration with 3 copies, -n4 for four copies, etc. > > cool, so with 16 drives, and say -n6 or -n8, and a far configuration - that gives a pretty good level of resistance to multi-disk failures, as well as an entire node failure (taking out 4 drives) which then leaves the question of whether the md driver, itself, can be failed over from one node to another Thanks! Miles -- In theory, there is no difference between theory and practice. In practice, there is. .... Yogi Berra