[OpenAFS] hard link behavior

Chas Williams (CONTRACTOR) chas@cmf.nrl.navy.mil
Tue, 06 Jul 2010 20:54:44 -0400

In message <20100707005602.v77jd7w14tcgwooo@www.umrk.nl>,Jaap Winius writes:
>For example, if it were possible to change the properties of a volume 
>so that only the ACL of the volume's root directory would apply to all 
>of its subdirectories, then in such cases there would never be any ACL 
>conflicts and the usual limitation that prevents hard links from being 
>created across directories could be suspended.

this would be fraught with peril to implement safely and isnt reversible.
say someone changes their mind about this acl policy.  should we go
through the entire volume fixing the hard links so they arent supposed
to be hard links?

>If this were possible, such volumes would be great for making 
>disk-based backups on. These solutions typically make heavy use of 
>hard links to save space, but the problem is that they are stuck on 
>the partitions on which they are created. But if they could be created 
>on an AFS volume, they could be moved to other partitions or servers 
>with ease. In addition, their contents could also be made available 
>via the AFS namespace. Sure, you'd still lose the AFS ACL information 
>when making these backups, but I wouldn't care much about that: even 
>without retaining the ACL information, this would still be a great way 
>to take advantage of AFS when making disk-based backups.

afs has a better scheme for this -- copy on write.  create a volume.
dump in your backup.  now vos clone that volume.  this would be a
snapshot of that backup.  future backups go into the original volume,
vos clone'ing as necessary for the snapshots in time.

this does have some limits.  vos clone is limited to 4 copies and you
cannot move those volumes off the same partition as the original.

instead of creating a special hardlinks mode perhaps expending beyond
the 7 slots for copy on write volumes would be more productive.