Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932603Ab3FQK37 (ORCPT ); Mon, 17 Jun 2013 06:29:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55855 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755062Ab3FQK34 (ORCPT ); Mon, 17 Jun 2013 06:29:56 -0400 Date: Mon, 17 Jun 2013 11:29:44 +0100 From: Joe Thornber To: OS Engineering Cc: "koverstreet@google.com" , "linux-bcache@vger.kernel.org" , "dm-devel@redhat.com" , LKML , Jens Axboe , Padmini Balasubramaniyan , Amit Phansalkar Subject: Re: Performance Comparison among EnhanceIO, bcache and dm-cache. Message-ID: <20130617102943.GA11121@debian> Mail-Followup-To: OS Engineering , "koverstreet@google.com" , "linux-bcache@vger.kernel.org" , "dm-devel@redhat.com" , LKML , Jens Axboe , Padmini Balasubramaniyan , Amit Phansalkar References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 863 Lines: 21 On Tue, Jun 11, 2013 at 03:05:07PM +0000, OS Engineering wrote: ... > Dm-cache commits on-disk metadata every time a REQ_SYNC or REQ_FUA > bio is written. If no such requests are made then it commits > metadata once every second. If power is lost, it may lose some > recent writes. Not true (though it is true for thinp, which may be where you got this idea?). For caching we have to commit whenever data is moved about, otherwise a crash could result in us reading data that is not just out of date (acceptable for some), but used to belong to a totally different part of the device (always unacceptable). - Joe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/