IBM DCAS-32160 - Ultrastar 2.1 GB Hard Drive, Specifications

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MF, Multiplication Factor determines how the Maximum Pre-fetch field is interpreted. When this bit is
set the data to pre-fetch is given by the command length multiplied by the value in the Maximum Pre-
fetch field. When this bit is reset the value in the Maximum pre-fetch field is used as the absolute length
to pre-fetch.
RCD, Read Cache Disable bit, of zero indicates that the file may return data requested by a R E A D
command by accessing either the cache or the Read Ahead Buffer, or media. A R C D bit of one indi-
cates that the file shall transfer all data requested by a R E A D command by accessing the media (i.e.,
data cannot be transferred from the cache or Read Ahead Buffer).
Read Retention Priority, Demand Read Retention Priority is not supported.
Write Retention Priority, Write Retention Priority is not supported.
Disable Pre-fetch Transfer Length specifies a number of LBA's which if a read command length exceeds
will cause the drive not to perform read ahead buffering after the command has completed. A value of
zero specifies read ahead is disabled.
Minimum Pre-fetch specifies the minimum number of LBA's that the drive should read ahead after each
read command. A value of zero indicates that read ahead should be terminated immediately a new
command arrives, except in the case when the new command is on the current head and track.
Maximum Pre-fetch specifies the maximum number of LBA's to read ahead after a read command. This
field can either be used as an absolute value, if the M F bit is 0, or else it will be multiplied by the read
command length to give the actual length to read ahead.
Maximum Pre-fetch ceiling specifies the maximum number of blocks the drive should attempt to read
ahead. It is particularly relevant when the M F bit is set.
Number of Cache Segments This field is used to indicate to the drive how many segments are requested
by the initiator. The target supports following Cache Segment configuration:
Note: When the Number of Cache Segments is set to 1, Tagged Command Queuing will be disabled
automatically and the multi-initiator environment will not be supported. If the Tagged Command
Queuing need to be supported, Number of Cache Segments 3 or 7 shall be selected.
Number of Seg-
ments
Segment Size
1 448K
3 128K
7 64K
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O E M Spec. of DCAS-34330/32160