From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gilad Arnold Subject: Re: migrating from RAID5 to RAID10 Date: Thu, 10 Jun 2010 15:26:26 -0700 Message-ID: <20100610222625.GA14165@libra.CS.Berkeley.EDU> References: <20100609151132.GA10082@libra.CS.Berkeley.EDU> <20100611005231.401529c0@natsu> <20100610195851.GA8408@libra.CS.Berkeley.EDU> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Drew Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Jun 10, 2010 at 03:11:43PM -0700, Drew wrote: > Actually No. If it is RAID-5 as you claim, then currently it is > effectively a RAID-0. > > RAID-5 is Striping with Distributed Parity and requires a *minimum* of > 3 disks. Two disks, regardless of how you got there, is considered > a degraded state. Sounds to me that you can still stripe and distribute parity with two drives, only that parity will amount to mirroring, and it can still tolerate a single drive failure. I got there in the usual way, creating a RAID5 with --raid-devices=2. --8<------8<------8<------8<------8<------8<------8<------8<------8<---- $ mdadm --detail /dev/md4 /dev/md4: Version : 0.90 Creation Time : Thu Nov 27 15:48:58 2008 Raid Level : raid5 Array Size : 484391808 (461.95 GiB 496.02 GB) Used Dev Size : 484391808 (461.95 GiB 496.02 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 4 Persistence : Superblock is persistent Update Time : Thu Jun 10 15:16:45 2010 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 64K UUID : 1da37f10:3c14071d:40784aba:8675d418 Events : 0.94324 Number Major Minor RaidDevice State 0 8 4 0 active sync /dev/sda4 1 8 20 1 active sync /dev/sdb4 --8<------8<------8<------8<------8<------8<------8<------8<------8<---- Gilad