About non-QIC tape drives on AIX
Variable length block and fixed length block refer to how the operating system reads from and writes to a tape. Variable-mode devices allow more flexibility to read previously written tapes. Many tape devices can be accessed in either mode. NetBackup assumes variable length for non-quarter inch cartridge (QIC) drives.
For more information, see the chdev(1) and smit(1) man pages and the system management guide. The smit application is the most convenient way to change from fixed to variable-length-block devices manually.
Warning:
For NetBackup, you must configure non-QIC tape drives as variable-length-block devices. Otherwise NetBackup can write data but may not be able to read it correctly. During a read, you may see a not in tar format error.
When you add a non-QIC tape drive to NetBackup, NetBackup issues the chdev command to configure the drive as a variable length block device. For reference, the following is the command that NetBackup uses to configure a drive for variable mode:
/usr/sbin/chdev -l Dev -a block_size=0
Dev represents the logical identifier for the drive (for example: rmt0 or rmt1).
Therefore, you do not have to configure the drive manually for variable mode.