HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 29
HP restricted
• All of these values may be subject to change.
• There is no retension facility.
Recommended support of log pages
Some of the media-related data items on the log pages are duplicates of data that is available
through the
READ ATTRIBUTES command using the Media Auxiliary Memory (MAM) access
specification. We recommend that you use MAM commands as the primary source for such data,
because this access method is portable to tape drives from other vendors, that is, the data is not in
a vendor-unique format.
In the long term, HP intends to expose all tape usage and drive hardware usage information via the
industry-standard MAM-format commands, so it is wise to start to implement this approach now.
For full details of the Ultrium log pages, see the
LOG SENSE command in Chapter 4, “Commands”,
of SCSI Interface, Volume 3 of the HP LTO Ultrium Technical Reference Manual.
Factors affecting performance
Further details on improving performance can be found in the “How to optimize the performance of
hp ultrium tape drives” white paper.
Host-related factors
Performance Factor Detail
Host SCSI performance The execution of each SCSI command involves a number of bus
phases, of which the data phase is only one.
The key phases are as follows:
• Intra-command bus-free time
• Arbitration and selection
• Message out
• Command
Host Burst Rate During the data phase of each SCSI command, data is transferred to
or from the drive at the host’s burst rate. If the host’s burst rate is slow,
then it takes longer to transfer the data. Extra time during this phase is
simply added to the total command time, and so it can affect the
overall performance.
Even if the burst rate is much faster than that required to maintain
streaming, the total command time may prevent the commands from
being issued fast enough.
