[OpenAFS-devel] Re: usage cases for vos create -id and -roid?

Jeffrey Hutzelman jhutz@cmu.edu
Sat, 25 Jul 2009 17:09:49 -0400


--On Saturday, July 25, 2009 03:39:46 PM -0500 Andrew Deason 
<adeason@sinenomine.net> wrote:

> The reason the options were created in the first place is because the
> inode numbers for files is based on the volume id they reside in.

You mean, the inode numbers reported by the OpenAFS UNIX cache manager to 
the operating system VFS layer (and thus to applications) for files 
residing in AFS.

> But that's not necessarily the only reason. Conceivably there could be
> some AFS-aware software that manipulates volumes based on volume id. Or
> maybe something caches volumes by ids, and you needed to remove/recreate
> one or something. That's just hypothetical, though; I'm not aware of
> anything that actually behaves like that, and doing something like
> organizing volumes by id just seems silly.

There might be obscure reasons for creating a new volume with a specific 
ID, but they'd be very obscure, and in general, using this option is 
dangerous.  A volume ID is part of the FID for files in that volume; if you 
delete the volume and create a new one with the same ID, then the files in 
it are not the same files and must not have the same FID's.  Violating this 
can result in clients having incorrect cached data and not knowing it, and 
that can lead to real data corruption, in which valid data on the server is 
overwritten with invalid data by a client.

-- Jeff