Frank Smith wrote:

Hi All

I have two dds3 tape changer units and would like to know if amanda can
use both of these units simultaneously. Can I do some sort of raid
backup across two tapes in two different machines of just use two tape
units at once.

I think the latest (2.4.3) release lets you stripe or mirror across
multiple tape drives one one machine (I remember reading it was a
feature of the betas, don't know for sure if it stayed in the final
release).  I don't think taper will write two different dumps to two
drives simultaneously.

Right.  With the 2.4.3 code you can stripe accross drives, set your
tapedev to "rait:{tape:/dev/rmt1,tape:/dev/rmt2,null:}"
which will do a RAID-4 stripe of the two tape drives and write the
parity blocks to the null tape device.  This should give you roughly
double the throughput and capacity, if your I/O isn't bottlenecked
(on some configurations and some drives you need to have the two
drives on their own SCSI bus to get double throughput; not sure about
DDS2...)  In this configuration you always need both tapes to be
able to read a backup.

If you want a mirrored tape, its "rait:{tape:/dev/rmt1,tape:/dev/rmt2}"
or more abreviatedly "rait:tape:/dev/rmt{1,2}", then you get two copies
of the tape.

Had you a third drive, you could do the 3-way RAID-4 stripe, and you could
read the backup with any two of the 3 tapes in the event of tape failure.

Marc