Use of tapes20
HP restricted
Tape status and capacity
Following autoload or a LOAD command, the software can determine the state of the tape and its
capacity from the Cartridge Memory and the Tape Capacity Log pages retrieved through the
LOG
SENSE
command. The information can also be invoked as a console operation at any time to find
the status and condition of the media.
Tape capacity figures can be used for two purposes:
• To give an application or user an indication of whether the tape has enough capacity for a
proposed backup. When using data compression, however, this is of little value, since the
compression factor cannot be predicted accurately.
• Periodically during a backup to give an approximation of the amount of tape left.
CAUTION: An application should not use the capacity reported in the Tape Capacity log to fix the
backup size. This will result in permanent capacity truncation that could represent a significant
percentage of the available capacity.
Finding the remaining capacity
Examine the Tape Capacity Log to estimate the effective remaining capacity of the tape
(data-compression factors are not considered).
Interpreting Log Sense data
The following points affect the values returned in the data:
Units Capacities are given in megabytes (1,048,576 bytes) of user data and assume no
compression.
General • If data compression is used, the capacities are specified as though the drive is in
pass-through mode. The data compression factor is not considered.
• Regions of tape used by the system, such as EOD areas, are not included in
capacities specified. In other words, values are conservative.
• An allowance for read-after-write retries is made.
Maximum
Capacity
Maximum capacity values are only valid when the tape has completed a load
sequence. If an immediate mode
LOAD is made, LOAD SENSE will not return valid
information until the tape has been successfully loaded and tape motion has ceased.
Remaining
Capacity
The remaining capacity value is the amount of tape remaining calculated from EOD.
Remaining capacity values are only valid after the successful completion of the
following commands in non-immediate mode:
LOAD LOCATE MODE SELECT READ REWIND
SPACE VERIFY WRITE WRITE FILEMARKS
The values after any subsequent command cannot be relied on unless the command
is a sense type that does not cause any tape motion.
