daily on-line backups (was Re: unix undelete ?????)

[Jonathan I. Kamens]

In article <563 at appserv.Eng.Sun.COM>, lm at slovax.Eng.Sun.COM (Larry McVoy) writes:
|> Most of this sort of thing goes away when you have a hierarchical file system
|> that saves the last days files as /yesterday.

  AFS does this (or, it can do this, if you configure your AFS setup to do
daily clones of volumes that should be backed up daily).  The big win with how
AFS does it is that it makes hard links to files rather than actually copying
them, and then only does copying of the cloned files when you change the (in
essence, it's copy-on-write for files).  The result is that the clone volume
takes up very little extra space on the disk, but accidentally changed or
removed files can be recovered.

  Now, for those of you who are saying, "What, AFS keeps file backups on the
same partition as the master copy?  What if the disk crashes," I'll point out
that AFS has *another* function, called "backup" rather than "clone," which
actually backs up a volume to another disk.  It can even be another disk on
another machine in another building.  In fact, there can be *several* backup
sites on several different machines and/or partitions.  And it only takes one
command to do the backup.  And you can configure things so that when you
reference files in a read-only volume, it will randomly pick one of the backup
volumes to get the file from (or, in more recent code, pick a volume on the
local subnet if there is one, or a volume randomly from another subnet if
not), thus distributing the load over the available backup volumes.

  Obviously, you can see that I think AFS does do some things right.  I won't
go into the problems I think it has. :-)

-- 
Jonathan Kamens			              USnail:
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