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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922fa96f0esm261148635e9.12.2026.06.18.02.59.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Jun 2026 02:59:08 -0700 (PDT) Date: Thu, 18 Jun 2026 10:59:06 +0100 From: David Laight To: Christoph Hellwig Cc: Eric Biggers , Andrew Morton , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-raid@vger.kernel.org Subject: Re: [PATCH v3] lib/raid/xor: x86: Add AVX-512 optimized xor_gen() Message-ID: <20260618105906.11033b70@pumpkin> In-Reply-To: <20260618092500.GC17530@lst.de> References: <20260615190338.26581-1-ebiggers@kernel.org> <20260617055653.GB19218@lst.de> <20260617110516.0a70950e@pumpkin> <20260618092500.GC17530@lst.de> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 18 Jun 2026 11:25:00 +0200 Christoph Hellwig wrote: > On Wed, Jun 17, 2026 at 11:05:16AM +0100, David Laight wrote: > > > FYI, one or 2 sources are basically useless as they RAID5 configs > > > that have no benefits over simple mirroring and thus the numbers > > > aren't too interesting. > > > > With three disks you xor two buffers (src_count == 1) to get the parity > > to write to the third - so that is a valid RAID5 config. > > Sure. It did not say it is invalid, it just isn't very useful. > It gives you 2/3 the total capacity, mirroring only gives 1/2. But for a lot of uses I suspect disks are cheap enough that mirroring is usually the 'best bet'. It also means that there are a set of catastrophic failures that can be more easily recovered. It is probably more important to ensure all the disks in a raid set come from different production lines - otherwise they are likely to fail at the same time. At least modern disks don't (seem to) suffer from 'sticky oil' which would tend to stop them restarting after they got cold while turned off. Raid doesn't help when multiple disks fail to start! David