From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55150) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f8nTE-0004Y9-Eg for qemu-devel@nongnu.org; Wed, 18 Apr 2018 09:50:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f8nTD-0008Vu-JD for qemu-devel@nongnu.org; Wed, 18 Apr 2018 09:50:00 -0400 References: <20180227155514.16721-1-eblake@redhat.com> <20180227162944.17343-2-eblake@redhat.com> <89477aaf-a1af-861d-fcd5-5bfe2143f8b8@redhat.com> From: Eric Blake Message-ID: <5430e92a-db1e-e853-e7d8-1b31cbfc0edc@redhat.com> Date: Wed, 18 Apr 2018 08:49:55 -0500 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dPKjYJMMpOLJSZ54fHoHi3GFKO0wQUSrr" Subject: Re: [Qemu-devel] [PATCH v4 2/5] qcow2: Document some maximum size constraints List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz , Alberto Garcia , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, kwolf@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --dPKjYJMMpOLJSZ54fHoHi3GFKO0wQUSrr From: Eric Blake To: Max Reitz , Alberto Garcia , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, kwolf@redhat.com Message-ID: <5430e92a-db1e-e853-e7d8-1b31cbfc0edc@redhat.com> Subject: Re: [PATCH v4 2/5] qcow2: Document some maximum size constraints References: <20180227155514.16721-1-eblake@redhat.com> <20180227162944.17343-2-eblake@redhat.com> <89477aaf-a1af-861d-fcd5-5bfe2143f8b8@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 04/13/2018 12:08 PM, Max Reitz wrote: >>>> With 512 byte clusters and 64 bit refcount entries I still get 8 PB,= >>>> way over what's limited by the L1/L2 tables (128 GB). >>> >>> Do I need to make any modifications to the sentence, then? >> >> I guess what surprised me the first time that I read it was that it >> suggests that this has to be taken into account when calculating the >> physical limits of an image, while in practice it can be ignored. >> >> You could say something like=20 >> >> Although the larger the cluster size, the larger the offsets that ca= n >> be covered by the refcount table, in practice these limits cannot be= >> reached because they are larger than the ones imposed by other data >> structures. >=20 > Are there any updates here? I guess I personally would just drop the > whole paragraph, because I think it really doesn't matter... Yeah, I need to post a v5 of this series now that 2.13 is nearly open. >=20 > Also note that the maximum file size of ext4 is 16 PB (for 4 kB blocks)= =2E > OK, it's bigger for XFS, but that still gives some perspective. >=20 > Also, long before anyone is going to complain about the specification > failing to mention that limit, they are going to complain that qemu > refuses to open their image (because of its limit on the reftable size)= =2E >=20 > Max >=20 >> although I'm sure that you can come up with a better wording than mine= :) >> >> Berto >> >=20 >=20 --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org --dPKjYJMMpOLJSZ54fHoHi3GFKO0wQUSrr Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlrXTQMACgkQp6FrSiUn Q2qTLAgAncTmDTUIzwGREGNyYZW+uGNCf/UVSN8XKteS6IH4GBYA6Uf7DrfbGeiw 8k8wLynC41tRshMtovoXPfKfk9Kt828gAHcv0AMSmJZJKAPczUiq6KftkBgIbK+D xeNMSJARzIS/xDtvNPxfi9BqYgQkmeGD1f5EZQzmo/OvcAFZG+l2oHXlQuYGLfwh uT/lFyV5MjRGcAke/NuL/Sty4zTNsBsvoEMGyvGqah1F/nWyAlHpCl6uasyCIafu I1vWIpALe/cxXcfTb17IEVPKuKC8kW2WQFHb8aTMD9URpDoUHtQWa86y8SfmQqz8 9vHc6BOmdfHEpFVSHP+Z50eDKDS+sQ== =LV+l -----END PGP SIGNATURE----- --dPKjYJMMpOLJSZ54fHoHi3GFKO0wQUSrr--