Specifications

16 IBM System z Personal Development Tool: Volume 3 Additional Topics
2.1 SCSI tape drives
In general, zPDT supports the use of SCSI tape drives. However, not all SCSI tape drives
may be usable. The usability depends on the exact tape drive model, the firmware level, the
firmware options selected, and the exact SCSI adapter (and firmware level) that is used. IBM
has tested a number of tape drives, but cannot guarantee that your tape drive will work. We
strongly suggest that you work with your zPDT supplier to understand your SCSI tape drive
circumstances.
SCSI tape drives may be used in two ways:
򐂰 The awsscsi device manager allows SCSI tape drives to be used by System z programs.
򐂰 Several Linux utilities that directly use SCSI tape drives are provided with zPDT. These
utilities are normally used when zPDT is not active. These utilities are not associated with
devmaps or a device manager.
2.1.1 The awsscsi device manager
Selected SCSI tape drives may be used as “real” tape drives during 1090 operation. The
awsscsi device manager is used and allows the SCSI tape drive to appear as a 3420, 3480,
or 3490 device. A typical devmap definition might be:
[manager]
name awsscsi 7000
device 581 3490 3490 /dev/sg5
The 7000 in this example is the arbitrary CUNUMBR operand. This example defines a tape
drive at address (device number) 581. If z/OS is being used, then the current z/OS IODF must
have a corresponding device (3490) defined for this address. (z/VM detects devices
dynamically and would find a 3490 at this address.)
Please note that the appearance to software (as a 3490 in the example above) may have no
direct relation to the actual SCSI device type. In this case /dev/sg5 might be a DLT drive, for
example, that has no physical characteristics of a 3490 drive.
1
The Linux device for the SCSI tape drive can be changed with the awsmount command. For
example,
$ awsmount 580 -u /dev/sg5 (disassociate sg5)
$ awsmount 580 -m /dev/sg3 (mount different drive)
The last operand of the device statement (/dev/sg5 in the example) denotes the SCSI device
to be used. Determining this operand is a bit complicated. Linux can address a SCSI tape
drive in three ways:
/dev/stN (where N starts at 0 and is incremented as needed)
/dev/nstN
/dev/sgN
The /dev/stN and /dev/nstN interfaces are for sequential tape devices. The first tape drive on
a Linux system would be /dev/st0; a second tape drive would be /dev/st1, and so forth. The
two forms, /dev/stN and /dev/nstN, differ only in whether a rewind is performed when the
device is closed.
2
The /dev/stN and /dev/nstN interfaces are used with the zPDT stand-alone
1
IBM did not formally test DLT drives.
2
The /dev/stN device automatically rewinds (whatever this may mean for the actual device) when the device is
closed. The /dev/nstN devices do not provide an automatic rewind.