IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

256 IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

processing until the current request for free frames has been satisfied. The process starts

when the VMM needs memory and the lrud process starts running to steal memory. During

the process the VMM will determine how many pages it needs to steal, including enough

pages to get above maxfree. By setting lru_poll_interval to 0 (default) you tell the lrud not to

poll. By setting this parameter to a value, say 5, tells the lrud to poll every 5 milliseconds. We

recommend that you start with a value of 5. IBM has a Techdoc on setting this parameter:

http://www.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/TD102303

Fibre Channel adapter settings

There are two Fibre Channel adapter (HBA) settings that can help performance. The following

command changes the maximum transfer size (max_xfer_size) and the maximum number of

commands to queue (num_cmd_elems) of an HBA (fcs0) upon the next system reboot.

chdev -l fcs0 -P -a max_xfer_size=0x200000 -a num_cmd_elems=400 -P

The default maximum transfer size is 0x100000. Consider changing this value to 200000 or

larger. These values are adapter dependent. This changes the maximum I/O size that the

adapter will support and it also increases the DMA memory area used for data transfers by

the adapter. When the max_xfer_size=0x100000, then the memory area is 16 MB, and for

other values it is 128 MB.

The default number of simultaneous I/Os the adapter will handle is 200. The maximum for a 2

Gb HBA is 2048.

Putting it all together

For AIX 5.2 and AIX 5.3, you should be using a 64-bit kernel and JFS2 unless there is a

application related reason not to. Here is a good place to start:

򐂰 Set maxperm and maxclient to just less than numperm and numclient (after all the

memory is used up).

򐂰 Set minfree = 120 x # CPUs or the default whichever is larger.

򐂰 Set maxfree = minfree + (j2_maxPageReadAhead (or maxpgahead) x # CPUs).

򐂰 Set j2_maxPageReadAhead to 1024 (this for

sequential read ahead only!).

򐂰 Set lru_poll_interval to 5.

򐂰 Use release behind mount options where it makes sense.

򐂰 Change the HBA settings.

7.9.2 HP-UX OS tuning for sequential I/O

For sequential I/O, HP-UX needs to turn on read ahead kernel options. A list of tunable kernel

parameters for HP-UX Release 11i can be found at:

http://docs.hp.com/en/TKP-90203/index.html

There are two different file system types for HP-UX, VxFS, and HFS. VxFS is preferred for

performance reasons.

VxFS read-ahead options

The kernel options for enabling read ahead for VxFS file systems are the following.

vxfs_max_ra_kbytes Maximum amount of read-ahead data, in KB, that the kernel may

have outstanding for a single VxFS file system

vxfs_ra_per_disk Maximum amount of VxFS file system read-ahead per disk, in KB