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: Tue, 17 Apr 2012 19:16:09 +0200 Message-ID: <20120417171609.GA2859@lazy.lzy> References: <4F8D228D.8060005@westcontrol.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4F8D228D.8060005@westcontrol.com> Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi David, > My current state is that I've got theory worked out and written up - > not just for triple parity, but for more parities as well. For some > of it, I've got Python code to test and verify the maths. It turns > out that triple parity can work well - but for quad parity the limit > is 21 data disks (using generators 2, 4, and 8), or up to 33 (using > for example 0x07, 0x35 and 0x8b as generators). Realistically, I > think triple parity is the limit for practical implementations. Why is that? An RS code (255,251) should be possible, like it is a (255,223). What's the limitation? I'm sure there is even a "RAID-96", which is (96,64). My wild guess would be that the generators must be chosen in some way. Have you had a look at the "par2" code? That seems to be capable of doing a parametric RS, even if in 16bit words. bye, -- piergiorgio