From mboxrd@z Thu Jan 1 00:00:00 1970 From: Luca Berra Subject: Re: RAID6 questions Date: Fri, 3 Jul 2009 08:40:03 +0200 Message-ID: <20090703064003.GC23464@maude.comedia.it> References: <2bdd5a4c0907020822s7d136681g23a4e34e13f0be8@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Return-path: Content-Disposition: inline In-Reply-To: <2bdd5a4c0907020822s7d136681g23a4e34e13f0be8@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Jul 02, 2009 at 05:22:54PM +0200, Marek wrote: >5. In case one decides for a partitioned approach - does mdadm kick >out faulty partitions or whole drives? I have read several sources >including some comments on slashdot that it's much better to split >large drives into many small partitions, but noone clarified in maybe because those suggesting this are not able to come up with a reasonable explanation? >detail. A possible though unlikely scenario would be simultaneous >failure of all hdds in the array: > > md1 RAID6 sda1[_] sdb1[_] sdc1[U] sdd1[U] sde1[U] sdf1[U] > md2 RAID6 sda2[U] sdb2[_] sdc2[_] sdd2[U] sde2[U] sdf2[U] > md3 RAID6 sda3[U] sdb3[U] sdc3[_] sdd3[_] sde3[U] sdf3[U] > md4 RAID6 sda4[U] sdb4[U] sdc4[U] sdd4[_] sde4[_] sdf4[U] > md5 RAID6 sda5[U] sdb5[U] sdc5[U] sdd5[U] sde5[_] sdf5[_] >(...) > >If mdadm kicks out faulty partitions only, but leaves the remaining >part of drive going as long as it's able to read it, would it mean >that even if every single hdd in the array failed somewhere (for >example due to Reallocated_Sector_Ct), mdadm would keep the healthy >partitions of that failed drive running, thus the entire system would >be still running in degraded mode without loss of data? This really depends on your priorities, i would have replaced my drives well in advance of a similar situation. The only reason i can imagine for splitting a disk into many partitions and raiding them together is avoiding lenghty rebuilds when a single drive is kicked from an array due to a correctable read error. In practice the above scenario should not happen anymore, since md will retry writing a stripe if it gets a read-error, besides you are planning on using raid6, so a single drive failure will still leave you with a nice degree of protection. Regards, L. -- Luca Berra -- bluca@comedia.it Communication Media & Services S.r.l. /"\ \ / ASCII RIBBON CAMPAIGN X AGAINST HTML MAIL / \