Hitachi HUS151473VL3800 - Ultrastar 73.4 GB Hard Drive Specifications page 144

ing segmentation.
• WCE (Write Cache Enable) bit when set at zero indicates that the drive must issue Good status for WRITE (6) or
WRITE EXTEND (10) command only after successfully writing the data to the media. When the WCE bit is set to
one, the drive may issue Good status for a WRITE (6) or WRITE EXTEND (10) command after successfully receiv-
ing the data but before writing it to the media. When WCE = 1, the drive operates as if AWRE = 1.
WCE is ingored when the DTDC field in Mode Page 2 is non-zero.
Note: When WCE = 1, a SYNCHRONIZE CACHE command must be done to ensure data are written to the media
before powering down the Target.
• MF (Multiplication Factor) bit determines how the Maximum and Minimum Pre-fetch parameters are interpreted. If this
bit is set to zero, the parameters are used as is. If the bit is set to one, the parameters are multiplied by the number of
blocks requested in the Read Command.
• RCD (Read Cache Disable) bit set at zero indicates that the drive may return some or all of the data requested by a
READ (6) or READ (10) command by accessing the data buffer, not the media. An RCD bit set at one indicates that
the Target does not return any of the data requested by a READ (6) or READ (10) command by accessing the data
buffer. All of the data requested is read from the media instead.
• Demand Read Retention Priority sets the retention priority of data requested on a Read command. It may be set as
defined below:
Value
0h Do not distinguish between requested data and other data
1h Replace requested data before other data.
Fh Replace other data before requested data.
where the value is the Demand Read Retention Priority or Write Retention Priority. Requested data is the blocks specified in
the Read or Write command. Other data is data in the cache from any other operation such as pre-fetch, read-ahead, etc.
If the Read Retention Priority is not set to Fh or if the DPO bit on the Read command is set to one, the requested data is over-
written by read-ahead data.
If the DPO bit is set to zero and the Read Retention Priority is set to Fh, the requested data is not overwritten with read-ahead
data. If the requested transfer is larger than the segment, the requested data is overwritten with more requested data and there
is no read-ahead
• Write Retention Priority sets the retention priority of data provided on a Write command. See the definition of
Demand Read Retention Priority above for more details.
• Disable Pre-fetch Transfer Length is used to prevent read-ahead after Read commands that are longer than the speci-
fied number of blocks. If this parameter is set to zero, a read-ahead is not performed.
• Minimum Pre-fetch specifies the minimum number of LBAs that the drive should read ahead after each READ com-
mand. A value of zero indicates that read ahead should be terminated immediately after a new command arrives,
except when the new command is on the current head and track.
• Maximum Pre-fetch specifies the maximum number of LBAs to read ahead after a Read command.
• Maximum Pre-fetch Ceiling specifies the maximum number of blocks the drive should attempt to read ahead. This field
is ignored.
• FSW (Force Sequential Write) is not supported and is ignored.
• LBCSS (Logical Block Cache Segment Size) bit when set to one indicates that the Cache Segment Size field units shall
be interpreted as logical blocks. When it is set to zero, the Cache Segment Size field units shall be interpreted as
Definition
Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification
126