From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45971) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYD5l-0008SB-Va for qemu-devel@nongnu.org; Tue, 23 Feb 2016 08:33:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aYD5g-0004Uv-RS for qemu-devel@nongnu.org; Tue, 23 Feb 2016 08:33:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59901) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYD5g-0004Uk-M6 for qemu-devel@nongnu.org; Tue, 23 Feb 2016 08:33:24 -0500 References: <1377446780-15360-1-git-send-email-wdongxu@linux.vnet.ibm.com> From: Eric Blake Message-ID: <56CC5FA2.80903@redhat.com> Date: Tue, 23 Feb 2016 06:33:22 -0700 MIME-Version: 1.0 In-Reply-To: <1377446780-15360-1-git-send-email-wdongxu@linux.vnet.ibm.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="qFFcs3lXm3KwpW79GbTjiSF97hdx0uAHx" Subject: Re: [Qemu-devel] [PATCH V20 0/7] add-cow file format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Dong Xu Wang , qemu-devel@nongnu.org Cc: kwolf@redhat.com, Fam Zheng , wdongxu@cn.ibm.com, stefanha@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --qFFcs3lXm3KwpW79GbTjiSF97hdx0uAHx Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Reviving an old thread for discussion purposes: On 08/25/2013 10:06 AM, Dong Xu Wang wrote: > It will introduce a new file format: add-cow. >=20 > The add-cow file format makes it possible to perform copy-on-write on t= op of > a raw disk image. When we know that no backing file clusters remain vi= sible > (e.g. we have streamed the entire image and copied all data from the ba= cking > file), then it is possible to discard the add-cow file and use the raw = image > file directly. >=20 > This feature adds the copy-on-write feature to raw files (which cannot = support > it natively) while allowing us to get full performance again later when= we no > longer need copy-on-write. Lately there has been discussion about a new external bitmap file format. I suspect everything in that conversation will make it possible to do anything that was planned by this (now-abandoned) series. But knowing all the use cases may help make sure we consider all the design aspects for what is needed if we track bitmaps of raw files in their own file format. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --qFFcs3lXm3KwpW79GbTjiSF97hdx0uAHx Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJWzF+iAAoJEKeha0olJ0Nqi+kH+gJu3YTzfVwT6qdGreuhsWeP fMGbZbXApifDTyCyyqAjqfsuEjUsWyXCvNI27flD9a1VxYSaSQAFv7IqorCk3cnQ iIU9AnDKjtEPvFYRWP0oIpwTemKef7fjnNNdG+PKIuNvT7A1zNJ0JzN5QWk1Ilsf R7ZqizwMy2yJkS01QeFcg41dRV9vjrpxpxSSk+/+1miLB+ytmke7wRmt/awChIBQ QLL/YLF/WKcD6TgH7b7/qNhCwnWcHZGDiRFNu4atStmosCph1SRChpM7yt8ak3au U2m3IX/W/pfi3tqUWseGryx/hvyxjZkoP6oE8rGzZVyn/+PsncyoUfJN5Ccj6nI= =23+A -----END PGP SIGNATURE----- --qFFcs3lXm3KwpW79GbTjiSF97hdx0uAHx--