From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:57112) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGG4T-000797-AU for qemu-devel@nongnu.org; Thu, 14 Mar 2013 17:52:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UGG4S-0007Og-4n for qemu-devel@nongnu.org; Thu, 14 Mar 2013 17:52:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:30917) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGG4R-0007Oc-TE for qemu-devel@nongnu.org; Thu, 14 Mar 2013 17:52:20 -0400 Message-ID: <51424690.3000100@redhat.com> Date: Thu, 14 Mar 2013 15:52:16 -0600 From: Eric Blake MIME-Version: 1.0 References: <1362867748-30528-1-git-send-email-stefanha@redhat.com> <1362867748-30528-5-git-send-email-stefanha@redhat.com> In-Reply-To: <1362867748-30528-5-git-send-email-stefanha@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="----enig2ITJUMSEGFFJJGHMTAWDR" Subject: Re: [Qemu-devel] [RFC 4/8] block: add block_backup QMP command List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , Markus Armbruster , qemu-devel@nongnu.org, dietmar@proxmox.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2ITJUMSEGFFJJGHMTAWDR Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 03/09/2013 03:22 PM, Stefan Hajnoczi wrote: > @block-backup >=20 > Start a point-in-time copy of a block device to a new destination. >=20 I'm trying to figure out how this is different from drive-mirror. If I understand correctly: After starting drive-mirror, a write to the block device is also written to the mirror, so that the destination sees the new data After starting block-backup, a write to the block device flushes the old data to the destination, so that the destination sees the old data Timing-wise, I can accomplish a backup through either command, with the following differences: With drive-mirror, I start a job, wait for it to hit sync'd state, then cancel the job. The copy is tied to the point where I cancel, and the moment I cancel, I no longer have to worry about keeping the destination writable (that is, the bulk of the copying is done prior to the point in time). With block-backup, I start a job, then wait for it to complete. The copy is tied to the point where I started the job, but as that may take some time, I have to keep the destination writable until the job completes (that is, the bulk of the work is done after the point in time)= =2E The concept is indeed useful; more so if we can wire this into 'transaction' to capture multiple disks at the same point in time. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org ------enig2ITJUMSEGFFJJGHMTAWDR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.13 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJRQkaQAAoJEKeha0olJ0NqQdsIAJj3zTYLg2FyYs61j35ZZ4qb r+MDwMWekQmgnfeVy79ROH+lGzdzE/f6iPe0a9N+Sqqp9cz8fP/ZOJBjCoRAofEy 0BK12UCrPwoXwYkyfNbV9GH5sUoGtA13t/wPZHl/wkOIBCW7xSyW1g9I+RbG3bsR ezaPuxIU6hHLJDGsllZCysu9P6DHRCJilPsqI5WSqeDPTd+m+/WfbqsHScpKbpc8 0spL6Z6xeGV1j333I4SNbM/7KLQC2jXnr/nci+GN6KHiPbjK6qkbO5dhEQP2jBzQ jFNgESL2Rp4ODcgNMEWcBOGamdkEO0wsDR9d/mjThSu4i9R6FCzpPMNHkjwyk8Q= =jIso -----END PGP SIGNATURE----- ------enig2ITJUMSEGFFJJGHMTAWDR--