202 POWER7 and POWER7+ Optimization and Tuning Guide
Queue information can be monitored in AIX 5L V 5.3 and later by running iostat –D. For AIX
5L V5.1 and AIX 5L V5.2, SAR can be used. Run qdepth_enable=no to use the hdisk wait
queue rather than the dpo device wait queue.
You should increase num_cmd_elems for the FC adapter from the default (initially starts at 400).
Some of these parameters require a system reboot to take effect.
Run the following commands to display and modify disk and adapter parameters
and settings:
Disk: max_transfer and queue_depth
– ‘lquerypv –M hdisk#’ displays the maximum I/O size a disk supports.
– ‘lsattr –El hdisk#’ displays the current disk values.
– ‘lsattr –R -l hdisk# -a max_transfer hdisk#” displays the allowable values.
– ‘chdev –l hdisk# -a max_transfer=value –P’ modifies the current disk values.
Adapter: max_xfer_size, lg_term_DMA, and num_cmd_elems
– ‘lsattr –El fcs#’ displays the current value.
– ‘chdev –l fcs# -a max_xfer_size=value -P’ modifies the current value.
SDD/DPO: qdepth_enable
– ‘lsattr –El dpo’ displays the current value.
–Run datapath to change the parameters if at SDD 1.6 or greater. Otherwise, run chdev.
For example:
‘datapath set qdepth disable’
Available documentation
For detailed tuning information, see the following publications:
Best Practices for Configuring your IO Subsystem for SAS9 Applications;
http://support.sas.com/rnd/papers/sgf07/sgf2007-iosubsystem.pdf
How to Maintain Happy SAS Users:
http://support.sas.com/resources/papers/happyIT.pdf
AIX limitations for I/Os: This is not an exhaustive description and does not detail all
possible AIX limitations for total number of I/Os. Also, carefully evaluate the queue
parameters before you implement any changes. For tuning guides specific to a particular
IBM storage system such as the IBM System Storage DS4000®, DS6000, or DS8000, see
Appendix B, “Performance tooling and empirical performance analysis” on page 155.
Device state: The device must be in an offline or disabled state before you change
any parameters, and then you must run cfgmgr.
Device state: The device must be in an offline or disabled state before you change
any parameters, and then you must run cfgmgr.
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