Subject: Re: Amanda backups: gtar or dump?
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: current-users
Date: 10/25/1998 17:33:08
> I've just finished setting up amanda here (been on my todo list for
> over a year :-) and am trying to decide whether I should use dump or
> gnu tar and would appreciate opinions of others.

My preference would be for dump, largely because it goes below the
filesystem.  (My tar can do likewise, but it's not very well suited to
incremental dumps, though I know at least one site using it for their
routine backups - though not with amanda.)

> I also noted that the example disklist shows a prefernce for
> compressing dumps - but my DAT (Seagate/Archive python) drive does
> compression so I assume its better to let the tape drive do it?

"It depends".

> Just letting the drive do compression would certainly help amanda
> with its tape space estimates.

Actually, it *impairs* amanda's tape space estimates - amanda really
would like to know what the compressed size of the dump is.  (Unless
you're using an amanda that knows how to query the tape drive to find
out where it is on the tape - as far as I know no such amanda exists,
but I'm relatively out of touch.)

Unless cpu crunch proves to be an unacceptable performance bottleneck,
amanda would probably prefer to compress on the hosts.  This (a)
improves the tape space estimates (see previous paragraph) and (b)
allows better compression because it can compress across more than one
tape block (tape-drive compression perforce has to compress each tape
record independently).  But if it's the difference between acceptable
and unacceptable wall-clock-time-to-dump, do what you have to. :-)

> Also, I was a bit reluctant to re-enable rsh on my systems - even
> though it is blocked at the ppp link.  Has anyone hacked amanda to
> use ssh?

The amanda I've used doesn't require rsh; it just happens to use the
same files (.rhosts) for its authorization tests.  (I don't think this
is *good*, mind you, just that it's what that amanda does.)

					der Mouse

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