Using DLT 4000 SCSI Tape Drive on SCO OpenServer 5

When doing cpio backups using the DLT 4000 SCSI tape drive under SCO OpenServer 5, it is important to specify a particular block size using the "-C" option. Whilst the device will still back up if this is not done, it will not stream in an efficient manner.

The effect of this is that its performance will be greatly reduced, with the result that backups can take up to 7 times longer than is actually necessary.

We therefore recommend that when cpio is invoked, the blocking factor is set to 10240 bytes to the record. We have tried greater values with no significant improvement in performance. A typical cpio instruction would be as follows:

# find . -depth -print|cpio -ovC10240 >/dev/rct0

In practice, this has resulted in a data transfer rate approaching 50Mb/min, as against some 7Mb/min when cpio uses its default blocking factor.

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