From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: Raid6 write performance Date: Sun, 01 Mar 2009 12:35:41 -0800 Message-ID: <49AAF19D.8050502@zytor.com> References: <49742E74.9090502@rabbit.us> <49A88DB4.40008@zytor.com> <6c4602af0903011112o440d7a4i22a24b58ada58865@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <6c4602af0903011112o440d7a4i22a24b58ada58865@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: =?UTF-8?B?TWljaGHFgiBQcnp5xYJ1c2tp?= Cc: Peter Rabbitson , linux-raid@vger.kernel.org List-Id: linux-raid.ids Micha=C5=82 Przy=C5=82uski wrote: >=20 > I'm afraid that might be incorrect. >=20 > Let's assume we want to write 100MB of data onto a 4 drive raid6. > Let's divide 100MB of data into two parts, say A and B, each 50MB big= =2E > Writing the data on the raid, would mean writing: > * A on disk1 > * B on disk2 > * XOR(A,B) on disk3 > * Q(A,B) on disk4 > That is actually assuming 50MB chunk, and whole chunk writes, etc. > Each of written portions would have been 50MB in size. That sounds > reasonable to me, as with 2 data disks, only half of data has to be > written on each. The fact that disks are really striped with data, XO= R > and Q doesn't change the image in terms of amount written. >=20 > I do hope I had understood the situation correctly, but I'll be ever > happy to be proved wrong. >=20 Ah, sorry, yes you're of course right. I was thinking about latency, not throughput, for some idiotic reason. -hpa --=20 H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- 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