HP LTO 4 SAS, LTO 4 FC, LTO 4 SCSI Recommended support of log pages, Factors affecting performance

•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.

HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 29 HP restricted