AWS 95 & A/UX: tc Driver and Specify the Tape Size

This article describes how the tc driver works with regard to block sizes and how to specify the exact size of the tape to tc from the command line.
The following command will create a tape on an Apple Workgroup Server (AWS) 95:

tar cvlbBf 16 4500 /dev/rmt/tc2 /MI48585

However, this command tells the driver the tape capacity is 2MB not 2GB. This is because the 'B' option argument is the number of 512 byte blocks in the active media. The DAT drive has about 2GB in capacity which is calculated as follows:

2*1024*1024*1024 = 2147483648 bytes.

Therefore the number of 512 byte blocks would be 4194304 and the command should be:

tar cvlbBf 16 4194304 /dev/rmt/tc2 /MI48585

The capacity of the DAT drive returned by the command, mt -f /dev/rmt/tc2 status, is 1992271053 bytes which is 3891154 blocks, so the tar command should be:

tar cvlbBf 16 3891154 /dev/rmt/tc2 /MI48585
Published Date: Feb 19, 2012