Also Sprach Marc Mengel:

> 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
>
>

What if you have 3 tape drives and would like to stripe data across
all three and throw away the parity? I tried the above syntax with
three tape devices and null: as the fourth and got:

ERROR: rait:{tape:/dev/nst2,tape:/dev/nst3,tape:/dev/nst4,null:}: reading
label: Numerical argument out of domain


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