Format-related factors, Recommendation

	Performance Factor	Detail
	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.

Format-related factors

	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.

32 Factors affecting performance

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