AIX Tip of the Week: Configuring Disks for Performance
Audience: Systems and Database Administrators
Date: September 3, 1999
There are three criteria for configuring disk drives: storage capacity,
price and performance. This tip addresses some of the performance
aspects of configuring disk drives. The guidelines are attached in a
MS Word document at the bottom of this page. The following list
summarizes some of the guidelines.
Application/Database Design: By far, the most important disk performance considerations are the design of the application and database. Both should designed to minimize I/O. Reconfiguring the disks to address issues with the application or database is rarely successful. The following guidelines assume there are no application or database issues.
Hardware: Provide sufficient hardware (memory, disks, adapters) to handle the I/O requirements. Size the number of disks and adapters to handle both I/O and storage capacity. Increase RS/6000 memory, which acts as a disk cache, to reduce I/O.
Configuration: Spread the I/O across as many disks and adapters as
economically feasible. Randomize the sequencing of the LV partitions
across the disks. Locate the most active partitions at the "optimum
spot" on the disk. Separate the most active partitions to dedicated
disks. To maximize serial performance, adjust AIX's vmtune's
"maxpgahead" and use Raid 0 (striping). To increase random write
performance, consider combining AIX LVM striping with Raid 5, or SSA
Raid 0 with AIX LVM Raid 1 (mirroring).
Operations: Serialize jobs that access the same data. Periodically run defragfs on write active JFS filesystems. Avoid I/O by turning off unnecessary logging.
Download the Disk Tuning Guidelines (MS Word format).