Re: [gentoo-user] filesystems

[Dirk Heinrichs <dirk.heinrichs@online.de>]

Am Montag, 24. November 2008 11:30:25 schrieb William Kenworthy:

> By transient storage I mean that the data is duplicated across across
> physical storage spaces so that if a machine goes down, the data is
> still available.

OK, thanks.

> I thought Andrews FS did that, but didnt see when
> looking at it yesterday.

Yes, (Open-)AFS indeed does this. However, this replication is read-only. This 
means you can read the data as long as at least one replica is available and 
write the data as long as the original (the read-write) volume is available. 
There are also some other things to keep in mind:

* AFS' primary tool for access control are its access control lists (ACL), but 
those are not posix, but AFS ACLs and they apply at the directory (not file) 
level. However, that's usually sufficient, because one can work with subdirs 
and symbolic links to implement more restrictive access for some files in the 
same directory.

* ACLs can also contain host names.

* If a volume is replicated, the client always prefers the read-only path 
(read-write volumes are usually accessed via /afs/.mycell.mydomain, while 
read-only volumes (if they exist) are accessed via /afs/mycell.mydomain). So 
if you want to modify a file you must explicitely open it via the rw-path.

* Replication doesn't happen automatically, needs an explicit command.

* Support for backup volumes is also there (comes with its own backup system).

* Can move volumes to different servers while online.

* Data is cached on the client.

* You'll need Kerberos 5.

If you have further questions, feel free to ask.

Bye...

	Dirk