Xdwrite (10) Command (50H) - Quantum Atlas 10K II 9.2/18.4/36.7/73.4 GB Product Manual

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 7
Byte
0
1
2 - 5
6
7 - 8
9
Figure 5–114 XDWRITE (10) Command Descriptor Block — Data Format
Table 5–108 XDWRITE (10) Command — Field Descriptions
Field
DPO
FUA
Disable Write
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives
6 5
Operation Code (50h)
Reserved DPO
Logical Block Address
Transfer Length
Description
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.
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.
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.
4 3 2
FUA Disable
Write
Reserved
Control
SCSI Description
1 0
Reserved
(continued)
5–231