[OpenAFS] Vos functions and clones and shadows

Dr A V Le Blanc Dr A V Le Blanc <LeBlanc@mcc.ac.uk>
Tue, 26 Jun 2007 09:37:46 +0100

In a recent discussion of clone and shadow volumes, Derrick Brashear
mentioned that the FAQ now contains some information about these.
My impression is that clone and shadow volumes give us an additional
possibility to do certain types of backup or quasi-backup operations.
But they are new enough not to be in the AFS documentation, and the
available information leaves some questions unanswered.

According to the FAQ, shadow volumes which are not live do not appear
in the VLDB.  Clones created by 'vos clone' are in the VLDB, but
they will be removed from the VLDB if a volume is deleted by
'vos remove'.  My question is, given a non-live shadow volume, or
a 'dangling clone', how do these behave when you run either
'vos syncserv' or 'vos syncvldb'?  I would guess that 'vos syncvldb'
ignores the shadow volumes (since their 'live' bit is not set)
and puts dangling clone volumes into the VLDB.  I would guess that
'vos syncserv' would remove a shadow which isn't live from the VLDB
if it found it there, but otherwise won't do anything.  Is that
what actually happens?

What if you create a shadow volume which has the same name as a
volume which exists elsewhere?  I assume that this would normally
work, since the shadow doesn't get into the VLDB.  If then you
made the shadow volume live, would it delete the VLDB entry for
the original volume?  Perhaps without deleting it from the other
disk?  If the shadow were on the same disk, would it not need to
delete the volume if the shadow with the same name became live?
or can you have a shadow with the same name on the same disk?

I would experiment, but things like this seem to have a good
chance of screwing up the VLDB, and I didn't much enjoy straightening
that out when it happened.

     -- Owen