What is random I/O?
Databases and general-purpose file servers are examples of random I/O environments. In random I/O, the time spent waiting for disk seeks and rotational latency dominates I/O service time.
Why do I need to know about random I/O?
You can optimize the performance of your configuration to take advantage of a random I/O environment.
What is the general strategy for configuring for a random I/O environment?
You want all disk spindles to be busy most of the time servicing I/O requests. Random I/O requests are small (typically 2-8 Kbytes), so it's not efficient to split an individual request of this kind onto multiple disk drives.
The interlace size doesn't matter, because you just want to spread the data across all the disks. Any interlace value greater than the typical I/O request will do.
For example, assume you have 4.2 Gbytes DBMS table space. If you stripe across four 1.05-Gbyte disk spindles, and if the I/O load is truly random and evenly dispersed across the entire range of the table space, then each of the four spindles will tend to be equally busy.
The target for maximum random I/O performance on a disk is 35 percent or lower as reported by DiskSuite Tool's performance monitor, or by iostat(1M). Disk use in excess of 65 percent on a typical basis is a problem. Disk use in excess of 90 percent is a major problem.
If you have a disk running at 100 percent and you stripe the data across four disks, you might expect the result to be four disks each running at 25 percent (100/4 = 25 percent). However, you will probably get all four disks running at greater than 35 percent since there won't be an artificial limitation to the throughput (of 100 percent of one disk).