HP LTO 4 SCSI, LTO 4 FC, LTO 4 SAS Time-out values, Media type identification, Maximum block size

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

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

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.

28 Factors affecting performance

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