From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: Adding Reed-Solomon Personality to MD, need help/advice Date: Thu, 29 Dec 2005 13:14:08 -0800 Message-ID: <43B451A0.1060601@zytor.com> References: <6.0.1.1.2.20040130235924.03f39710@mail.athenet.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: jeff@jab.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Jeff Breidenbach wrote: >>The fundamental problem is that generic RS requires table lookups even >>in the common case, whereas RAID-6 uses shortcuts to substantially >>speed up the computation in the common case. > > > If one wanted to support a typical 8-bit RS code (which supports a max of > 256 drives, including ECC drives) it is already way too big to use a table. RS > is typically done with finite field math calculations which are - > relatively - fast > but they are much heavier than a parity calculation. Here is one commercial > benchmark, note the throughput numbers at the bottom of the page. > Well, most of them are implemented via tables (GF log table, etc.) They tend to perform poorly on modern hardware. -hpa