Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752654AbYCJIYE (ORCPT ); Mon, 10 Mar 2008 04:24:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751319AbYCJIXy (ORCPT ); Mon, 10 Mar 2008 04:23:54 -0400 Received: from phunq.net ([64.81.85.152]:50875 "EHLO moonbase.phunq.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751316AbYCJIXx (ORCPT ); Mon, 10 Mar 2008 04:23:53 -0400 From: Daniel Phillips To: Grzegorz Kulewski Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet Date: Mon, 10 Mar 2008 00:23:51 -0800 User-Agent: KMail/1.9.5 Cc: linux-kernel@vger.kernel.org References: <200803092346.17556.phillips@phunq.net> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200803100123.51395.phillips@phunq.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1393 Lines: 28 On Monday 10 March 2008 00:51, Grzegorz Kulewski wrote: > > If UPS power runs out while ramback still holds unflushed dirty data > > then things get ugly. Hopefully a fsck -f will be able to pull > > something useful out of the mess. (This is where you might want to be > > running Ext3.) The name of the game is to install sufficient UPS power > > to get your dirty ramdisk data onto stable storage this time, every > > time. > > Are you using barriers or ordered disk writes with physical sync in the > right moments or something like that? I think this is needed to allow any > journaling filesystem to do it's job right. Usual block device semantics are preserved so long as UPS power does not run out before emergency writeback completes. It is not possible to order writes to the backing store and still deliver ramdisk level write latency to the application. After the emergency writeback completes, ramback is supposed to behave just like a physical disk (with respect to writes - reads will still have ramdisk level latency). No special support is provided for barriers. It is not clear that anything special is needed. Daniel -- 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/