Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753823AbYCOU0p (ORCPT ); Sat, 15 Mar 2008 16:26:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752625AbYCOU0h (ORCPT ); Sat, 15 Mar 2008 16:26:37 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:3320 "EHLO spitz.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752643AbYCOU0g (ORCPT ); Sat, 15 Mar 2008 16:26:36 -0400 Date: Sat, 15 Mar 2008 21:26:25 +0100 From: Pavel Machek To: Daniel Phillips Cc: David Newall , david@lang.hm, Chris Friesen , Alan Cox , linux-kernel@vger.kernel.org Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet Message-ID: <20080315202625.GC4193@ucw.cz> References: <200803092346.17556.phillips@phunq.net> <200803131232.07879.phillips@phunq.net> <47D9856E.9010304@davidnewall.com> <200803131303.04118.phillips@phunq.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200803131303.04118.phillips@phunq.net> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1347 Lines: 29 On Thu 2008-03-13 12:03:03, Daniel Phillips wrote: > On Thursday 13 March 2008 12:50, David Newall wrote: > > Daniel Phillips wrote: > > > The period where you cannot access the data is downtime. If your script > > > just does a cp from a disk array to the ram device you cannot just read > > > from the backing store in that period because you will need to fail over > > > to the ramdisk at some point, and you cannot just read from the ramdisk > > > because it is not populated yet. > > > > Wouldn't a raid-1 set comprising disk + ramdisk do that with no downtime? > > In raid1, write completion has to wait for write completion on all > mirror members, so writes run at disk speed. Reads run at ramdisk > speed, so your proposal sounds useful, but ramback aims for high > write performance as well. raid1 + kflushd tweak? special raid1 mode that signals completion when it hits _one_ of the drives, and does sync when the slower drive is idle? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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/