Drive queue depth

For performance reasons, you might want to change the disk command queue depth. The disk queue depth limits the maximum number of commands that AIX® software can issue concurrently to that disk at any time. Increasing a disk queue depth might improve disk performance by increasing disk throughput (or I/O) but might also increase latency (response delay). Decreasing a disk queue depth might improve disk response time but decrease overall throughput. The queue depth is viewed and changed on each individual disk. When changing the disk queue depth, the command elements and data transfer window on the parent adapter might also need to be changed.

System software allocation is supported for the following AIX software levels:

AIX Version 7.1 with Service Pack 3, or later
AIX Version 6.1 with the 6100-06 Technology Level, and Service Pack 5, or later
AIX Version 6.1 with the 6100-05 Technology Level, and Service Pack 6, or later
AIX Version 6.1 with the 6100-04 Technology Level, and Service Pack 10, or later
AIX Version 5.3 with the 5300-12 Technology Level and Service Pack 4, or later
AIX Version 5.3 with the 5300-11 Technology Level and Service Pack 7, or later

Viewing the drive queue depth

To view the current queue depth on any disk (JBOD or RAID), use the lsattr command from the AIX command line.

The queue_depth attribute contains the current setting. The default value for the disk queue depth is determined by the adapter family.

Table 1. Drive queue depth for different adapter families
	PCI-X and PCIe adapter family	PCIe2 and PCIe3 adapter families
Default JBOD disk queue depth	16	16
Default RAID disk queue depth	4 times the number of pdisks in the RAID array	16 times the number of pdisks in the RAID array

Example

To list the current queue_depth attribute value for the hdisk2 disk, type the following command:

lsattr -E -l hdisk2 -a queue_depth

The system displays a message similar to the following: queue_depth 64 Queue DEPTH True

Last updated: Wed, May 24, 2017