74 xpwrite (10) command, Xpwrite (10) command – Seagate Fibre Channel Interface User Manual
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Fibre Channel Interface Manual, Rev. D
12.74
XPWrite (10) command
The XPWrite (10) command requests that the target xor the data transferred with the data on the medium and
then write the xor data to the medium.
If the logical unit is reserved, a reservation conflict occurs when a XPWrite command is received from an initia-
tor other than the one holding the logical unit reservation. The command is rejected with Reservation Conflict
status if the reservation conflict is due to a logical unit reservation. The XPWrite command is evaluated for
extent reservation conflicts. XPWrite commands with a reservation conflict is terminated with Check Condition
status and the sense key is set to Data Protect with the appropriate additional sense code for the condition if
any part of the XPWrite operation is prohibited by an extent reservation.
Field definitions (listed alphabetically)
Control
See Section 11.2.1.6.
DPO (Disable Page Out)
The DPO bit is used to control replacement of logical blocks in the cache memory when the host has information on the
future usage of the logical blocks.
1
The disc drive assigns the logical blocks accessed by this command the lowest priority for being fetched into or
retained by the cache. The host knows the logical blocks accessed by the command are not likely to be accessed
again in the near future and should not be put in the cache memory nor retained by the cache memory.
0
The host expects that logical blocks accessed by this command are likely to be accessed again in the near future.
FUA (Force Unit Access)
1
The target accesses the media in performing the command prior to returning Good status. Read commands access
the specified logical blocks from the media (i.e., the data in not directly retrieved from the cache). In the case where
the cache contains a more recent version of a logical block than the media, the logical block is first written to the
media.
0
The target satisfies the command by accessing the cache memory. For read operations, any logical blocks that are
contained in the cache memory are transferred to the initiator directly from the cache memory.
Logical Block Address
The starting logical block address where the target reads data from its medium. This field also specifies the starting logical
block address where the xor result data is written to the medium.
Transfer Length
The number of blocks that will be read from or written to the medium.
Table 239: XPWrite (10) command (51h)
Bit
Byte
7
6
5
4
3
2
1
0
0
0
1
0
1
0
0
0
1
1
Reserved
DPO
FUA
Reserved
2
3
4
5
(MSB)
Logical Block Address
(LSB)
6
Reserved
7
(MSB)
Transfer Length
8
(LSB)
9
Control
51h
Table
number