HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 31
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Drive-related factors
Recommendation: • Try not to put Ethernet in the way of data transfer unless staging
technology is being used; aggregation of multiple Ethernet clients
remains a good strategy to delivering on drive performance.
• Even with Gbit Ethernet, the effective throughput is less than that of
an LTO Ultrium 4 drive, so either use carefully designed topologies,
or stage an image first and use locally attached tape, otherwise the
Ethernet itself can become the bottleneck.
Gbit Ethernet can be used in a carefully designed topology.
Alternatively, stage an image first and then use locally attached tape
for the backup.
Write Commands Do not interleave write commands with other commands, such as
READ
POSITION
and LOG SENSE. Do not, for example, attempt to read the
TapeAlert log page during a long write.
Performance Factor Detail
Performance Factor Detail
Drive’s SCSI
Performance
In order to minimize SCSI bus loading, the drive must execute its SCSI
phases quickly. The phases are as follows:
• Selection
• Message-out identification
• Receipt of the command
• Disconnection
• Mid-command bus-free time
• Arbitration and reselection
• Message-in identification
Recommendation: The host must always ensure the following:
• Disconnects are enabled
• Synchronous negotiation is enabled and established between the
drive and the HBA
• The drive is in buffered mode
• When reading and verifying, always use the same block size as
that in which the tape is written, otherwise performance will be very
seriously affected.
Transfer Mode The transfer mode can be fixed or variable, selectable through the
MODE SELECT command.
Fixed Mode: The transfer size is equal to the (block) size multiplied by
the number of records (blocks) in the transfer.
