From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from frost.carfax.org.uk ([85.119.82.111]:60081 "EHLO frost.carfax.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751279Ab3LQRUR (ORCPT ); Tue, 17 Dec 2013 12:20:17 -0500 Date: Tue, 17 Dec 2013 17:20:02 +0000 From: Hugo Mills To: David Howells Cc: Simon Wilkinson , jaltman@your-file-system.com, "openafs-devel@openafs.org" , linux-btrfs@vger.kernel.org, clm@fb.com Subject: Re: What is needed to build an AFS fileserver on top of BTRFS? Message-ID: <20131217172002.GE11281@carfax.org.uk> References: <14884.1387299196@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Oiv9uiLrevHtW1RS" In-Reply-To: <14884.1387299196@warthog.procyon.org.uk> Sender: linux-btrfs-owner@vger.kernel.org List-ID: --Oiv9uiLrevHtW1RS Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Dec 17, 2013 at 04:53:16PM +0000, David Howells wrote: > It has occurred to me and others that something like BTRFS could be > a good fit to build an AFS fileserver directly on top of. The > question is what facilities would be needed from BTRFS to make this > work? So I thought I'd kick off a shopping list;-) > (1) 64-bit data version numbers that increase monotonically with > each write. Yes, this is likely to cause some performance > degredation as it introduces an ordering over data writes and > metadata writes to a file. Maybe writes can be batched to improve > performance? Do these have to be per-file? If not, then you might be able to get away with using the transid, which is a filesystem-global monotonically-increasing number. btrfs batches disk writes already, and uses the transid to differentiate these -- the writes come at 30 second intervals (by default, although there's an option to change the period). There may be multiple distinct changes to a single file within that transaction (although obviously, only the state of the file after the last one gets written to disk). I don't know exactly what you need it for, so this may or may not be appropriate here. Ceph uses transids for [something, mumble, wavy-hand] -- I don't know if the use-case for Ceph is equivalent to the use-case for AFS. > (2) Storage for ACLs and AFS UIDs. Having shareable ACLs might also > be useful. Xattrs would likely do for this. This would seem like a reasonable place to put them, given that that's what POSIX ACLs do, and we have POSIX ACL support already. > (3) The ability to snapshot a filesystem to make backups and for > pushing to read-only volume servers. We have snapshots of subvolumes, but not the filesystem as a whole. > (4) A 32-bit vnode number and 32-bit vnode uniquifier/generation > number. These don't necessarily have to be stored by BTRFS directly > but could instead be in a separate database file that gets > snapshotted also. > > (5) The ability to set the vnode number, vnode uniquifier and data > version number to specific values. Necessary to clone volumes > and restore volume dumps. What's a vnode meant to represent? I'm not familiar with the terminology. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- "Are you the man who rules the Universe?" "Well, I --- try not to." --Oiv9uiLrevHtW1RS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.14 (GNU/Linux) iQIVAwUBUrCHwlheFHXiqx3kAQJkJw//Rby5HNleZkZx0aiGrcMKxQ63m6IBUtuT xHGrZgGIc0uhU3Z3hnjSUS462IN1tHRcpB380UXjoxjrNWkghHIGWzuduQ0K63OR a1pRzgOcseWWoAqy79q/D5/2yWrmZZSPObTgKGAifzkvPGwEUdphg6TndnO/jUfQ 7sTwtyID30H3aOy88pmiW0/RAk/T6ri3TA4V39XydvlxBYFlEUJPuL0N/NxCiImG RBNv1x5Gwzm57jgs0PqEwchodSKopzaCMAi89fmpSYyGKOatNngadU5eF1MICjpU 2yw5mcoZt32EOu1t30egwLd3K1hcJymCz+9aG6et2rtNa4fogL1RJBFrQFjT6Nm/ JbCL1ChSvX1xD7WRPI3D5SmCFF2Rbmu6AXEy6/HJsoQdBWq/KbJjv8kc/PEZqxix w09ELd7OsjC/DjX8ONTZeH0ZZ+NEI5sUnd9V98OSPqmE/TPpMzpUa1FSTe8SusRE xZhaVaOIr0yeoDDxrzAC3lKcN+FecfnEUWF3CX+xqSGeB327ywW0N+W7HL3o7W+F BMAupy9dwSGthOgndl4vF3MDPvZgszXl1LsLdtC0hALEX4zrTP448EnBO0AmB+hJ V5giHuTWz+ATVAyQMhYGDyeoEBNFvCn976kQkoLa2o5iRu091TzGuQzvsKkbJO3n 11TaxxzFxNI= =TcMC -----END PGP SIGNATURE----- --Oiv9uiLrevHtW1RS--