SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–231
5.54 XDWRITE (10) COMMAND (50h)The XDWRITE (10) command requests that the target XOR the data transferred
with the data on the medium. The resulting XOR data is stored in the target’s
buffer. The disposition of the data transferred from the initiator is controlled by the
Disable Write bit.
The resulting XOR data remains in the target’s buffer until it is retrieved by an
XDREAD command with staring Logical Block Address and transfer length fields
that match the starting Logical Block Address and transfer length of the XDWRITE
command.
Bit
Byte
76543210
0Operation Code (50h)
1Reserved DPO FUA Disable
Write Reserved
2 - 5 Logical Block Address
6Reserved
7 - 8 Transfer Length
9Control
Figure 5–114 XDWRITE (10) Command Descriptor Block — Data Format
Table 5–108 XDWRITE (10) Command — Field Descriptions
Field Description
DPO Disable Page Out. When the value = 0, the drive
caches the data read, using its normal Logical Read
Unit Policies.
When the value = 1, the drive assigns to logical blocks
accessed the lowest priority for being fetched into or
retained by the cache.
FUA Force Unit Access. When the value is 0, the drive is
allowed to satisfy the read with cache-resident data.
A value of 1 indicates that the drive accesses the
media in performing the command.
Disable Write A Disable Write bit of 0 indicates that the data
transferred from the initiator is to b e written to the
medium after the XOR operation is complete. A
Disable Write bit of 1 indicates that the data will not
be written to the medium. If the Disable Write bit is set
to 1, the FUA bit is ignored.
(continued)