Choosing A Blocking Factor Or A Block Size; Tape Utilities - Sun Microsystems SPARCstorage Library Installation And User Manual

D

Choosing a Blocking Factor or a Block Size

Tape Utilities

mt
D-4
You must use the proper block size in the data transfers to the tape drive. The
block size determines the amount of data sent to the drive in one command
and, more importantly, determines the amount of data on each logical block on
the drive.
You get the best performance and throughput when you use the largest block
size (blocking factor) supported. Typically, this is 63k bytes which is specified
as a blocking factor of 126. The b parameter and a numerical parameter are
specified in the command to the drive. A block size must be specified on both
the write and the read operation. If one is not selected, a default is used that
may not be the largest or best choice. Be aware that the read operation must
always specify an equal or larger block size than the write operation. There is
no penalty for choosing a larger block size on read. Thus, you should always
choose the largest block size for any read operation.
Note – Loss of data can occur if the commands described in the following
paragraphs are used inappropriately. This information is provided as a guide
for experienced system administrators.
Refer to the System Administrators Handbook for more detailed information
about using these commands.
A very useful set of capabilities is incorporated in the mt command. The basic
format of this command is to type mt -f /dev/rmt/0 subcommand. The
most relevant subcommands supported are: status, rewind, and offline. To
access the on-line man page, type man mt.
SPARCstorage Library Installation and User's Guide—June 1995