[rescue] Re: how to utilize multiple tape drives in the same library/silo with Amanda...

[Kurt Mosiejczuk]

> > Ahh, thanks for reminding me of another amanda killer on real FSs.  Amanda
> > wants a FS as big as your biggest FS to buffer in.  That's irrational on
> > most real sized (.5tb+) file systems.

The reason it wants the space is that the thing that takes longest is
tape access.  Particularly if you dribble date in at less than the full
tape rates.  If your tape can do 5MB/sec and you dribble in 4.5MB/sec
then the tape drive keeps on buffering it up and stopping and starting.
Stopping and starting REALLY slows stuff down.  The scratch space
allows AMANDA to queue up multiple backups and then dd them to the tape
at full tape speed.  It saves LOTS of time.  However, you need that
scratch space.  It will work without, but it then defaults to
streaming it from the network to the tapedrive.  And then you hit
those problems with not enough data to keep the tape working.

--Kurt