From mboxrd@z Thu Jan 1 00:00:00 1970 From: Drew Subject: Re: migrating from RAID5 to RAID10 Date: Thu, 10 Jun 2010 15:21:27 -0700 Message-ID: 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=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids >> No, it is not degraded, it's a clean 2-drive RAID5. I know it doesn'= t >> make much sense as it is ;-) =C2=A0the intent was to grow the array = later, >> relying on mdadm's grow feature. Right now, I'm guessing that it >> operates like a RAID1 for all practical purposes. > > 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* o= f > 3 disks. Two disks, regardless of how you got there, is considered a > degraded state. Actually, I need to retract those statements. A clean two disk RAID-5 array can be created and is actually very similar to a RAID-1 array. =46rom this thread: http://ubuntuforums.org/archive/index.php/t-566803.= html --- If you're using just 2 disks in a non-degraded setup, then you'll have the following structure Drive1 Drive2 Block1: A1 P1 Block2: P2 B1 Block3: C1 P3 Block4: P4 D1 In this case, you're parity blocks will actually be identical to your non-parity blocks. This is because P1 is calculated as P1 =3D A1 XOR ?? Since there is no other block to XOR your bits with, md falls back to ?? =3D 0, and we all know that the XOR of 0 is the identity. That is, P= 1 =3D A1 XOR 0 =3D=3D A1 --- I stand corrected. :-) --=20 Drew "Nothing in life is to be feared. It is only to be understood." --Marie Curie -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html