From mboxrd@z Thu Jan 1 00:00:00 1970 From: Piergiorgio Sartor Subject: Re: Is this enough for us to have triple-parity RAID? Date: Fri, 20 Apr 2012 23:01:06 +0200 Message-ID: <20120420210106.GA2432@lazy.lzy> 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> <4F91B1C4.5080205@hesbynett.no> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <4F91B1C4.5080205@hesbynett.no> Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: Alex , "H. Peter Anvin" , linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi again David, > Yes, being a generator for GF(2^8) is a requirement for a parity > generator (sorry for the confusing terminology here - if anyone has > a better suggestion, please say) to be part of a 255 data disk > system. However, being a GF generator is necessary but not > sufficient - using parity generators (1, 2, 4, 16) will /not/ give > quad parity for 255 data disks, even though individually each of 1, > 2, 4 and 16 are generators for GF. I ask again, could you please elaborate this? I nowhere found such a further constrain for the parities. All I could find is that the Vandermonde matrix must be done with generators. > 255 data disks is the theoretical limit for GF(2=E2=81=B8). But it i= s a > theoretical limit of the algorithms - I don't know whether Linux md > raid actually supports that many disks. I certainly doubt if it is > useful. The reason to use many disks is in case of geo-redundant RAID, for example with iscsi. In this situation you want to have a lot of redundance, in parities, not mirror. bye, --=20 piergiorgio -- 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