Procedure
-
Enable DASD statistics for the device of interest.
Example:
# dasdstat -e dasdc
enable statistic "/sys/kernel/debug/dasd/dasdc/statistics"
-
Assure that I/O requests are directed to the device.
Hints:
- Access a partition, rather than the whole device, to avoid directing the I/O request towards the
first 2 tracks of a CDL formatted DASD. Requests to the first 2 tracks of a CDL formatted DASD are
exceptional in that they never use High Performance FICON.
- Assure that a significant I/O load is applied to the device. PAV aliases are used only if
multiple I/O requests for the device are processed simultaneously.
Example:
# dd if=/dev/dasdc1 of=/dev/null bs=4k count=256
-
Look for PAV and HPF in the statistics.
Example:
# dasdstat dasdc
--------------------------------------------------------------------------------
statistics data for statistic: dasdc
start time of data collection: Fri Dec 11 14:22:18 CET 2015
7 dasd I/O requests
with 4000 sectors(512B each)
3 requests used a PAV alias device
7 requests used HPF
In the example, dasdc uses both Parallel Access Volume and High
Performance FICON.
