Factors affecting performance32
HP restricted
Format-related factors
Recommendation: A good transfer size to aim at is 256 KB (128 KB minimum). For an
application that uses 512-byte records, each fixed-mode transfer
should transfer 512 records. Higher transfer sizes are also
recommended for higher compression ratios.
Variable Mode: Only one block is transferred at a time. The size of the
block determines the size of the transfer. Ideally the application should
aim to use 256 KB blocks.
Records (Block) Size The size of the transfer impacts the performance, rather than the size of
the record (blocks) in the transfer.
Recommendation: As above, aim to use 256 KB transfers. Higher transfer sizes are also
recommended for higher compression ratios.
Transfer Size Transfer size is the amount of data transferred for a single command,
whether the drive is in fixed or variable block mode.
In both fixed and variable modes, the drive works best if it receives a
large amount of data for each command, so a large transfer size for
write commands is recommended.
At small block size, the transfer rate is substantially degraded. This is
because the drive controller and the host spend too much time
handling SCSI overhead instead of writing data to tape, resulting in
stream-fails. The block size at which this happens varies between
drives, but generally the faster the drive, the larger the block size
needed to stream.
Recommendation: Use 256 KB transfers as a minimum. Higher transfer sizes are also
recommended for higher compression ratios.
Transfer Direction There are some noticeable performance differences between reads
and writes, caused by the extra device CPU time needed by the drive
to read data sets from the media.
Recommendation: Use large transfer sizes; the drive is less likely to stream-read small
transfer sizes than it will when writing transfers of the same sizes.
Performance Factor Detail
Performance Factor Detail
Tapemarks Tape marks (filemarks) have many different uses to give a logical
structure to data on a tape. The SCSI Standard specifies certain actions
that the drive must take when it is told to write a filemark.
If the drive is told to write a filemark when the Immediate bit is not set,
the standard insists that the drive must flush all data to tape. If used
unnecessarily this will adversely affect performance and waste tape
capacity.
Recommendation: Write filemarks as rarely as is reasonable for your application.
