From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: Is this enough for us to have triple-parity RAID? Date: Thu, 19 Apr 2012 11:16:48 -0700 Message-ID: <4F905690.3060301@zytor.com> References: <4F8D228D.8060005@westcontrol.com> <20120417171609.GA2859@lazy.lzy> <4F8DD02F.1060504@westcontrol.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4F8DD02F.1060504@westcontrol.com> Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: Piergiorgio Sartor , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 04/17/2012 01:18 PM, David Brown wrote: >=20 > For quad parity, we can try g3 =3D 8 as the obvious next choice in th= e > pattern. Unfortunately, we start hitting conflicts. To recover miss= ing > data, we have to solve multiple simultaneous equations over G(2=E2=81= =B8), whose > coefficients depend on the index numbers of the missing disks. With > parity generators (1, 2, 4, 8), some of these combinations of missing > disk indexes lead to insoluble equations when you have more that 21 d= isks. >=20 That is because 255 =3D 3*5*17... this means {02}^3 =3D {08} is not a g= enerator. -hpa -- 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