From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Subject: Re: Is this enough for us to have triple-parity RAID? Date: Fri, 20 Apr 2012 10:27:08 +0800 Message-ID: References: <4F8D228D.8060005@westcontrol.com> <20120417171609.GA2859@lazy.lzy> <4F8DD02F.1060504@westcontrol.com> <4F905690.3060301@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4F905690.3060301@zytor.com> Sender: linux-raid-owner@vger.kernel.org To: "H. Peter Anvin" Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids I think when David says 'generator', he doesn't mean the generator of t= he order 8 Galois field, he means an arbitrary set of number in it which can re= nder the system of equations solvable to up to a certain number of data disks(not necessarily 255). He uses a brute-force method with the help of a Python program to= actually figure that out. It looks pretty cool to me since I have known the system of 4 equations generally fails to render a solution for a while, but now I know exactly how many ways it may fail... Cheers, Alex On Fri, Apr 20, 2012 at 2:16 AM, H. Peter Anvin wrote: > On 04/17/2012 01:18 PM, David Brown wrote: >> >> For quad parity, we can try g3 =3D 8 as the obvious next choice in t= he >> pattern. =C2=A0Unfortunately, we start hitting conflicts. =C2=A0To r= ecover missing >> 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. =C2=A0= With >> parity generators (1, 2, 4, 8), some of these combinations of missin= g >> disk indexes lead to insoluble equations when you have more that 21 = disks. >> > > That is because 255 =3D 3*5*17... this means {02}^3 =3D {08} is not a= generator. > > =C2=A0 =C2=A0 =C2=A0 =C2=A0-hpa > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at =C2=A0http://vger.kernel.org/majordomo-info.ht= ml -- 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