HP StorageWorks Command View SDM Installation and User Guide (T1086-96023, February 2005)

Command Line User Interface 163
Command Line User Interface
Number of Forced Unit Access
Commands
ARRAY
LUN
The number of host read and write commands processed
while the Forced Unit Access condition was in effect.
When the Forced Unit Access condition is in effect for a
read command, any data in the read cache addressed by
the read command is discarded and fetched from disk
again. When the Forced Unit Access condition is in effect
for a write command, any data in the write cache for the
LUN addressed by the write command is posted to disk
before the write command is processed. When the write
command is processed it is posted to disk before
completion status is reported to the host. The table below
indicates when the Forced Unit Access condition is in
effect.
Usage
Normally read commands that address data completely
contained in the read cache will be satisfied by reading
the data from the read cache rather than from disk.
Normally write commands will report completion after the
write data has been placed into the write cache and
before it is written to disk. The Forced Unit Access
condition causes host reads to be satisfied from disk and
host writes to be written to disk before completion is
reported to the host. Operating in Forced Unit Access
mode can significantly reduce performance, especially for
writes.
Firmware releases HP13 and prior Firmware releases after HP13
Array mode FUA requested in read FUA in effect? FUA in effect?
or write command?
Normal No No No
Normal Yes Yes No
Extended Normal No No No
Extended Normal Yes Yes Yes
Secure N/A Yes Yes
Table 12 Performance Metrics (Continued)
Metric Categories Description/Usage