From: Leonard, Roger (
Date: Thu Mar 18 1999 - 09:54:25 CST

Many thanks to Jonathan Goldthorp for his quick and concise response. My
original question was:

> I have 2 tape drives in my sparcenter 2000. One is identified upon
> bootup
> in the messages file as a Exabyte-8500 8mm and the other is a Archive
> Python
> 4mm. How do you determine what format and compression levels these
> drives
> support?

Jonathan wrote:

When you stick a tape into the drive and issue the command mt status
it'll tell you what's there:

# mt -f /dev/rmt/1 status
Exabyte EXB-8500 8mm Helical Scan tape drive:
   sense key(0x0)= No Additional Sense residual= 0 retries= 0
   file no= 0 block no= 0


# mt status
HP DDS-3 4MM DAT tape drive:
   sense key(0x6)= Unit Attention residual= 0 retries= 0
   file no= 0 block no= 0

(This is my default device hence no -f flag).

For DAT tapes you have three types of unit, DDS, DDS-2, DDS-3. Each tape
offers more compression, but costs more. In a DDS-3 you can use a DDS-2
and DDS tape but you won't get the same level of compression, in a DDS-2
you can use a DDS.

Each DAT offers the following levels of compression:

Format Length Capacity Capacity (Compression)

DDS 60mm 1.3 Gbytes 2.6 Gbytes
DDS 90mm 2.0 Gbytes 4.0 Gbytes
DDS-2 120mm 4.0 Gbytes 8.0 Gbytes
DDS-3 125mm 12.0 Gbytes 24.0 Gbytes

The device you use will depend on the SCSI id of the unit, one of your
units will be /dev/rmt/0 the other will be /dev/rmt/1. You don't have to
specify which type of device to use, the system can decide for you - for
example if you want compression you don't have to use /dev/rmt/0c - you
can use /dev/rmt/0 and the device driver will decide the maximum storage
that you can get.

For your Exabyte unit you have:

Low-Density (8200) about 3.5 GB
High-Density (8500) about 7.0 GB
Compression Mode (8500) about 14.0 GB

(I'm nor 100% sure of the capacity of the exabytes).

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