From: Jamie Lokier Subject: Re: [Qemu-devel] Re: Notes on block I/O data integrity Date: Wed, 26 Aug 2009 19:57:55 +0100 Message-ID: <20090826185755.GF25726@shareable.org> References: <20090825181120.GA4863@lst.de> <90eb1dc70908251233m4b90ddfuabb4d26bccd62c63@mail.gmail.com> <20090825193621.GA19778@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Javier Guerra , rusty@rustcorp.com.au, kvm@vger.kernel.org, qemu-devel@nongnu.org To: Christoph Hellwig Return-path: Received: from mail2.shareable.org ([80.68.89.115]:45846 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752654AbZHZS54 (ORCPT ); Wed, 26 Aug 2009 14:57:56 -0400 Content-Disposition: inline In-Reply-To: <20090825193621.GA19778@lst.de> Sender: kvm-owner@vger.kernel.org List-ID: Christoph Hellwig wrote: > > what about LVM? iv'e read somewhere that it used to just eat barriers > > used by XFS, making it less safe than simple partitions. > > Oh, any additional layers open another by cans of worms. On Linux until > very recently using LVM or software raid means only disabled > write caches are safe. I believe that's still true except if there's more than one backing drive, so software RAID still isn't safe. Did that change? But even with barriers, software RAID may have a consistency problem if one stripe is updated and the system fails before the matching parity stripe is updated. I've been told that some hardware RAID implementations implement a kind of journalling to deal with this, but Linux software RAID does not. -- Jamie