Seagate Ultra160 Product Manual page 236

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[17] The Force Sequential Write (FSW) bit, when set to one, indicates that multiple block writes are to be trans-
ferred over the SCSI bus and written to the media in an ascending, sequential, logical block order. When
the FSW bit equals zero, the target is allowed to reorder the sequence of writing addressed logical blocks
in order to achieve a faster command completion.
[18] The Logical Block Cache Segment Size (LBCSS) bit is not used at this time.
[19] The Disable Read-Ahead (DRA) bit, when set to one, requests that the target not read into the buffer any
logical blocks beyond the addressed logical block(s). When the DRA bit equals zero, the target may con-
tinue to read logical blocks into the buffer beyond the addressed logical block(s).
[20] The NUMBER OF CACHE SEGMENTS byte gives the number of segments into which the host requests
the drive divide the cache.
[21] The CACHE SEGMENT SIZE field indicates the requested segment size in bytes. This manual assumes
that the Cache Segment Size field is valid only when the Size bit is one.
[22] The NON-CACHE SEGMENT SIZE field, when greater than zero, specifies to the target the number of
bytes the initiator requests that the target allocate for a buffer function when all other cache segments are
occupied by data to be retained. If the number is at least one, caching functions in the other segments
need not be impacted by cache misses to perform the SCSI buffer function. The impact of the NON-
CACHE SEGMENT SIZE equal 0 or the same of this field plus the CACHE SEGMENT SIZE greater than
the buffer size is vendor-specific.
In addition to the caching control provided by the Caching Mode page, some 10-byte commands contain con-
trol bits DPO and FUA the intent of which is to override the cache page control bits.
DPO: Disable Page Out.
If DPO = 1, the cache replacement algorithm should not replace existing cache data with the current data (if
possible). If a cache segment must be overwritten, it should be made the LRU.
FUA: Force Unit Access.
Read: If FUA = 1, the requested data must be read from the media. If cache data which overlaps the request
has not yet been written to the media, it should be written before the read is allowed to occur.
Write: If FUA = 1, all data must be written to the media before the SCSI operation returns the status and com-
pletion message bytes.
SCSI Interface Product Manual, Rev. B