From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.saout.de ([127.0.0.1]) by localhost (mail.saout.de [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id mu0X1ElXcTWN for ; Mon, 3 Dec 2012 02:10:07 +0100 (CET) Received: from mps1.wohnheimg.uni-frankfurt.de (mps1.wohnheimg.uni-frankfurt.de [141.2.118.239]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.saout.de (Postfix) with ESMTPS for ; Mon, 3 Dec 2012 02:10:06 +0100 (CET) Received: from p4fcef7ed.dip.t-dialin.net ([79.206.247.237] helo=[192.168.0.51]) (Authed sender Sven 'DarKRaveR' Eschenberg) by mps1.wohnheimg.uni-frankfurt.de via ESMTPSA (TLSv1:CAMELLIA256-SHA:256) (Exim) (envelope-from ) id 1TfJt4-00070j-VI for dm-crypt@saout.de; Mon, 03 Dec 2012 01:27:56 +0100 Message-ID: <1354494476.2156.15.camel@laptop> From: DarKRaveR Date: Mon, 03 Dec 2012 01:27:56 +0100 In-Reply-To: <50B13522.1000003@gmail.com> References: <50AEF7B3.4000807@babioch.de> <20121123060720.GA5520@tansi.org> <2fffc2e10dfbf0a7ccaaf2ef43213a4e.squirrel@ssl.verfeiert.org> <50B13522.1000003@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [dm-crypt] Reconsidering default options for cryptsetup-reencrypt List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: dm-crypt@saout.de Sorry for the late reply, just a small followup. What you are saying Milan, is absolutely true, but for misaligned HW Raid setups, a huge block size together with O_DIRECT will bypass the OS'es caching strategy and the controller (knowing the actual layout) has a way better chance of compensating unnecessary IO with it's optimized write back caching (in the linear read-modify-write case of reenrypt). For rather small block sizes (near the size of a RAID stripe) in a misaligned case, such a compensation/elimination of unneeded IO is much harder. So small blocksize, lack of topology information, misalignment -> approx 50% loss in performance (as surveilled by opener) Regards -Sven On Sat, 2012-11-24 at 21:59 +0100, Milan Broz wrote: > On 11/24/2012 06:01 PM, Sven Eschenberg wrote: > > > BTW, what exactly are you referring to, when you talk about 64 MB blocksize? > > Here cryptsetup-reencrypt is in principle simple program, it reads a "block" > and write it back to device with new encryption parameters (and optionally with > some different offset). So block here is meant as an unit which is handled in one > reencryption step. > (But the real atomic unit of encryption is still 512B block of course.) > > There is no requirement this block to be aligned to underlying hw alignment > (but if it is misaligned, the same performance degradation problems apply of course). > > Milan > _______________________________________________ > dm-crypt mailing list > dm-crypt@saout.de > http://www.saout.de/mailman/listinfo/dm-crypt