Re: Perfomance problem backupscript (more details and tests)

On Mon, 2005-10-10 at 04:13, Joerg Schilling wrote:
> >
> > Depending on why the original died and what I wanted to have when I got
> > done rebuilding, changing filesystem types and/or mount points might be
> > a good thing.  Certainly the ability to make those decisions at restore
> > time is a good thing. 
> 
> Well, you told me that you use Amanda. A decent Backup control system should
> be able to be able to handle your problem together with a backup system.

Yes, but the GNUtar incremental mode has fewer constraints than dump
or star.  Amanda can work with dump, but then you have to work on
filesystem boundaries and make the restore mount topology exactly
match the source.

> -	The usual way for a backup is to backup whole filesystems.
> 
> 	However, star allows you to backup _partial_ filesystems if you
> 	care about the constraints. The constraints are that (on a fully
> 	POSIX compliant system) no directory from outside the scoped area
> 	may be renamed _into_ the scoped area and (in case ctime is not
> 	following POSIX rules) no _file_ is moved from outside the scoped
> 	area _into_ the scoped area.

Exclusions are important.  For example I never back up /var/spool/squid
but that seems to fit your constraint since I can count on nothing being
renamed in or out of the cache.

> -	If you are talking about mount points inside a _logigal_ area, then
> 	any part of a directory tree that is below the mount point is
> 	a complete filesystem to backup.

The piece I consider a valuable difference for gnutar is that it would
be reasonable to back up a single file system (for example where /home
and /var are included as part of /) and restore it to a different
topology, perhaps with /home and or /var as mount points.  Gnutar
would only have issues with hardlinks spanning the filesystems which
are unlikely to exist in cases like that. The rest of what happens
in an incremental restore would still work correctly.  The other
advantage of tar-style file handling is that I would expect less
to go wrong with changing portions when backing up active filesystems.

> You are either a backup operator that knows what he is doing (and does the right
> things by hand) or you use a decent backup control software.

With amanda, you can either let it tell you what tapes to insert or
you can strip off it's headers and work with the raw dump or gnutar
archives directly.

> BTW: The Amanda people did tell me that they would start to implement support
> for star once incrementals are posssible. If you like to use amanda, how about
> asking the amanda crew about a new version that supports star?

It has been quite a while since I've visted the amanda mailing list but
I'll try if anyone is still working on it.  It should be straightforward
to convert the dump driver code to use star instead.  It would also be
nice to have the acl-handling ability added to backuppc which can use
tar as it's underlying transport.

--
   Les Mikesell
    [email protected]