IBM Ultrastar 36LZX Specifications page 113

the WCE bit is set to one, the drive may issue Good Status for a Write(6) or Write extend(10) com-
mand after successfully receiving the data but before writing it to the media. When WCE = 1, the
drive operates as if AWRE = 1.
Note: When WCE = 1, a Synchronize Cache command must be done to assume data is written to
the media before powering down the Target.
Ÿ 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.
Ÿ 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.
Ÿ Demand Read Retention Priority sets the Retention Priority of data requested on a Read
Command. It may be set to 0h, 1h, or Fh as defined below.
Value 0h : Do not distinguish between Requested Data and Other Data.
Value 1h : Replace Requested Data before Other Data.
Value Fh : Replace Other Data before Requested Data.
The Value is the Demand Read Retention Priority or Write Retention Priority. Requested Data are
the blocks specified in the Read or Write Command. Other Data are data in the cache from any
other operation such as Pre-fetch or Read-Ahead.
If the Read Retention Priority is not set to Fh or if the DPO bit on the Read command is one, the
Requested data is overwritten by Read-Ahead data.
If the DPO bit is 0 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.
Ÿ Write Retention Priority sets the Retention Priority of data provided on a Write Command. It may
be set to 0h, 1h, or Fh. See definition of Demand Read Retention Priority above for more details.
Ÿ Disable Pre-fetch Transfer Length specifies a number of LBA's which if exceeded by a read
command length will cause the drive not to perform read ahead buffering after the command has
completed. A value of zero specifies read ahead is disabled.
Ÿ 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
after a new command arrives, except when the new command is on the current head and track.
Ÿ 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 MF bit is set at zero, or it will be multiplied
by the read command length to give the actual length to read ahead.
Ÿ Maximum Pre-fetch ceiling specifies the maximum number of blocks the drive should attempt to
read ahead. It is particularly relevant when the MF bit is set.
Ÿ FSW (Force Sequential Write) is not supported and internally ignored by the Target.
Ÿ 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 bytes.
Ÿ DRA (Disable Read Ahead) bit when set to one requests that the target not read into the buffer any
logical block beyond the addressed logical block(s). When it is set at zero, the target may continue to
read logical blocks into the buffer beyond the addressed logical block(s).
Ultrastar 36LZX hard disk drive specifications
113