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 11:32:27 +0800 Message-ID: References: <4F8D228D.8060005@westcontrol.com> <20120417171609.GA2859@lazy.lzy> <4F8DD02F.1060504@westcontrol.com> <4F905690.3060301@zytor.com> <067e21e2-6f21-48a7-93a8-bb2249534155@email.android.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <067e21e2-6f21-48a7-93a8-bb2249534155@email.android.com> Sender: linux-raid-owner@vger.kernel.org To: "H. Peter Anvin" Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids I understand we need a generator to facilitate a 255 data disks array, = but 255 sounds like a theoretic limit to me. ZFS now only supports an array of = only 9 disks(6 of them are data disks), so having, say, a quad-parity array of 48 disks(theoretically) doesn't sound that bad, does it? Cheers, Alex On Fri, Apr 20, 2012 at 11:00 AM, H. Peter Anvin wrote: > Being a generator is a requirement for that. > > Alex wrote: > >>I think when David says 'generator', he doesn't mean the generator of >>the order >>8 Galois field, he means an arbitrary set =C2=A0of number in it which= can >>render 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= the >>>> pattern. =C2=A0Unfortunately, we start hitting conflicts. =C2=A0To= recover >>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= =A0With >>>> parity generators (1, 2, 4, 8), some of these combinations of >>missing >>>> disk indexes lead to insoluble equations when you have more that 2= 1 >>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-rai= d" >>in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at =C2=A0http://vger.kernel.org/majordomo-info.= html > > -- > Sent from my mobile phone. Please excuse brevity and lack of formatti= ng. -- 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