Re: What is needed to build an AFS fileserver on top of BTRFS?

[Chris Mason <clm@fb.com>]

On Tue, 2013-12-17 at 16:53 +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?
>
>  (2) Storage for ACLs and AFS UIDs.  Having shareable ACLs might also be useful.
> 
>      Xattrs would likely do for this.
> 
>  (3) The ability to snapshot a filesystem to make backups and for pushing to
>      read-only volume servers.
> 
>  (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.

Hmmm, what exactly are vnodes?  Could we put them in xattrs?

-chris