Jon LaBadie <jon AT jgcomp DOT com> writes:

> If you do not use a holding disk, the dumps go straight to disk, making
> your fastest speed the slowest of dumping, compressing, and tape writing.
> And no other dump can be collecting in preparation for writing to tape.

Jon points out many other reasons why holding disks are
useful, and I agree.  But there is another reason that applies even in
a single-host environment.

In my experience tape drives (DDS anyway) are more reliable if they
are only used in streaming mode.  I think it's much harder on the
mechanism to be starting and stopping all the time.  With a holding
disk, the tape doesn't move until the dump is done and then the tape
writes at tape speed steadily the whole time with only occasional
start/stop.  So, my belief is that a holding disk is good insurance
against tape drive repairs, even if that's the only reason to have it
-- I wouldn't run amanda without it if at all possible.

Note that even a system with a large disk can use a partition as the
holding disk, particularly if you don't back up one partition (I tend
to have / /var /usr/home /n0, where /n0 is not backed up).

        Greg Troxel <gdt AT ir.bbn DOT com>