From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KLKBa-0005iN-7L for qemu-devel@nongnu.org; Tue, 22 Jul 2008 11:53:58 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KLKBV-0005g2-ED for qemu-devel@nongnu.org; Tue, 22 Jul 2008 11:53:57 -0400 Received: from [199.232.76.173] (port=39514 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KLKBV-0005fw-3r for qemu-devel@nongnu.org; Tue, 22 Jul 2008 11:53:53 -0400 Received: from mail2.shareable.org ([80.68.89.115]:42863) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1KLKBU-0002xm-NF for qemu-devel@nongnu.org; Tue, 22 Jul 2008 11:53:52 -0400 Received: from jamie by mail2.shareable.org with local (Exim 4.63) (envelope-from ) id 1KLKX1-00066O-Bb for qemu-devel@nongnu.org; Tue, 22 Jul 2008 17:16:07 +0100 Date: Tue, 22 Jul 2008 17:16:07 +0100 From: Jamie Lokier Subject: Re: [Qemu-devel] qcow2 - safe on kill? safe on power fail? Message-ID: <20080722161607.GA22535@shareable.org> References: <47CF0E0C.9030807@quinthar.com> <47CF16C5.6040102@codemonkey.ws> <20080721181031.GA31773@shareable.org> <4884E6F1.5020205@codemonkey.ws> <48850A99.7070005@codemonkey.ws> <48857926.5020708@qumranet.com> <4885EA8B.5050908@codemonkey.ws> <4885F068.2060902@qumranet.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4885F068.2060902@qumranet.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org > It's a simple matter of allocating, making sure the allocation is on > disk, and recording that allocation in the tables. The simple implementations are only safe if sector writes are atomic. Opinions from Google seem divided about when you can assume that, especially when the underlying file or device is not directly mapped to disk sectors. -- Jamie