Factors affecting performance28
HP restricted
absolute block size, performance should not suffer, but do ensure that the transfer size is at least
256 KB.
Maximum block size
The READ BLOCK LIMITS command indicates that block sizes and variable length transfer sizes are
supported for values between 1 byte and 16,777,215 bytes.
Media type identification
HP recommends that you use the REPORT DENSITY SUPPORT command (with the Media bit enabled)
to identify the type of media loaded in the drive.
Using Cartridge Memory instead of tape headers
For optimum performance, it is also important that the host writes application tape header
information to the Cartridge Memory (see “Cartridge Memory (LTO-CM)” on page 35) rather than
to the actual tape. This allows cartridges to load and unload quickly and prevents excessive media
wear at the beginning of the tape. As the access method to Cartridge Memory data is an open
standard, it also permits other software systems to identify alien media positively in shared storage
environments.
Using the Performance Log page for diagnosing problems
The Performance Log page (34h) contains data that should allow application software to monitor
the data-rate being sent to the drive dynamically. For details, see the
LOG SENSE command in
Volume 3, SCSI Interface, of the HP LTO Ultrium Technical Reference Manual.
Time-out values
Notes:
• These values are for a single SCSI command in non-Immediate mode. As most commands will
be sent in Immediate mode, status will be received by the host typically within 20 ms. In such
cases, the time-out given indicates when the drive will have completed the operation and be
ready for the next tape movement command.
SCSI Command Recommended Time-Out Value
Load 10 minutes
Unload 10 minutes
Rewind (full tape length) 10 minutes
Space/Locate/CD-ROM Read (10) 20 minutes
Erase (long) 5 hours
Erase (short) 5 minutes
Write/Write Filemarks 5 minutes
Read 20 minutes
Read/Write Attribute (MAM), with 1 KB of attribute data 1 minute
Non-tape movement (such as TEST UNIT READY, INQUIRY) 1 minute
