Seagate ST3285N, Руководство по эксплуатации продукта

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Byte 2
continued When the
Multiplication Factor (MF) bit is 0, the drive
interprets the minimum prefetch and maximum prefetch
fields as the number of logical blocks to be prefetched.
When the MF bit is 1, the drive interprets the minimum
prefetch and maximum prefetch fields in terms of a num-
ber which, when multiplied by the transfer length of the
current command, yields the number of logical blocks to
be prefetched.
When the Read Cache Disable (RCD) bit is 0, the drive
may return data requested by a Read command by ac-
cessing either the cache or the media. If the RCD bit is 1,
the cache is not used.
Byte 3 The
demand read retention priority field is not used. The
initiator cannot assign any special retention priority to the
drive.
The
write retention priority field is not used. The initiator
cannot assign any special retention priority to the drive.
Bytes 4–5 The disable prefetch transfer length always has a value
of FFFF
H
, which means that the drive attempts an antici-
patory prefetch for all Read commands.
Bytes 6–7 The minimum prefetch field specifies the minimum num-
ber of blocks the drive prefetches, regardless of the delays
it may cause in executing subsequent pending com-
mands. When the minimum prefetch field contains 0, the
drive terminates prefetching whenever another command
is ready to be executed. If the minimum prefetch equals
the maximum prefetch, the drive prefetches the same
number of blocks regardless of whether there are com-
mands pending.
Bytes 8–9 The maximum prefetch field specifies the maximum num-
ber of blocks the drive prefetches during a Read com-
mand if there are no other commands pending. The
maximum prefetch field represents the maximum amount
of data to prefetch into the cache for any single Read
command.
Bytes 10–11 The maximum prefetch ceiling field should be equal to the
maximum prefetch field. The maximum prefetch ceiling
and maximum prefetch fields are the same if the MF bit
is 0.
Byte 12 When the Force Sequential Write (FSW) bit is 1, the drive
writes blocks of data to the media sequentially, from
lowest to highest logical block address. When the FSW
bit is 0, the drive changes the sequence in which it writes
logical blocks to speed processing.
104 ST3655 Family SCSI Drives Product Manual, Rev. A