From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from asav4.altibox.net ([81.167.36.153]:58569 "EHLO asav4.altibox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751585Ab3KUIg6 (ORCPT ); Thu, 21 Nov 2013 03:36:58 -0500 Message-ID: <528DC628.9090403@hesbynett.no> Date: Thu, 21 Nov 2013 09:36:56 +0100 From: David Brown MIME-Version: 1.0 To: Andrea Mazzoleni CC: "H. Peter Anvin" , linux-raid@vger.kernel.org, linux-btrfs@vger.kernel.org, David Smith Subject: Re: Triple parity and beyond References: <528A90B7.5010905@zytor.com> <528AA1EB.3010909@zytor.com> <528B3A6F.2010304@hesbynett.no> <528C8F8E.9030908@hesbynett.no> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 20/11/13 19:34, Andrea Mazzoleni wrote: > Hi David, > >>> The choice of ZFS to use powers of 4 was likely not optimal, >>> because to multiply by 4, it has to do two multiplications by 2. >> I can agree with that. I didn't copy ZFS's choice here > David, it was not my intention to suggest that you copied from ZFS. > Sorry to have expressed myself badly. I just mentioned ZFS because it's > an implementation that I know uses powers of 4 to generate triple > parity, and I saw in the code that it's implemented with two multiplication > by 2. > Andrea, I didn't take your comment as an accusation of any kind - there is no need for any kind of apology! It was was merely a statement of fact - I picked powers of 4 as an obvious extension of the powers of 2 in raid6, and found it worked well. And of course, in the open source world, copying of code and ideas is a good thing - there is no point in re-inventing the wheel unless we can invent a better one. Really, I /should/ have read the ZFS implementation and copied it! mvh., David