Grass Valley Network Attached Storage System Serial ATA Network User Guide v.1.0.04 - Manual (Page 151)

Chapter 10 RAID System Administration
150 Digital News Production
Minimum
Prefetch 2048 disk blocks Minimum prefetch has two functions. It is the minimum
prefetch size, as per the SCSI specification, and it
specifies a low water value at which the controller
schedules prefetches. When the multiplication factor is
disabled, this is the number of blocks. When the
multiplication factor is enabled, this is a scalar multiple
of the transfer length of the current command. In both
cases, the number of blocks beyond the end of the current
request required in cache is the larger of this value or 2 x
(request size). If there are not enough blocks in cache,
the controller schedules a prefetch. The size of this
prefetch is the larger of the minimum prefetch or the
maximum prefetch. If discontinuity is disabled, the
prefetch size is truncated to end on a cache segment
boundary. If discontinuity is enabled, the prefetch size is
not truncated.
Maximum
Prefetch 4096 disk blocks The maximum prefetch is the maximum number of
blocks that the controller can prefetch. This field can be
overridden by both the multiplication factor and the
maximum prefetch ceiling.
Maximum
Prefetch Ceiling 16384 disk
blocks This is the upper limit for the number of blocks that can
be prefetched. If the computed prefetch is greater than
this ceiling, prefetch is truncated to this value.
(Multiplication factor does not affect this ceiling.)
Disable Prefetch
Transfer Length 4096 disk blocks The disable prefetch transfer length is the maximum
number of blocks for which prefetch is operational. A
Read command with a length greater than this value will
not allow a Read ahead. If this value is 0, prefetch is
entirely disabled.
Field Default Description