When it comes to choosing hard drives, there are several measures of performance that may influence your decision.

An important parameter for overall drive performance is revolutions per minute (abbreviated rpm, RPM, r/min, or r·min⁻¹); this is the speed at which the disk platters spin.  High rpms mean data passes the read/write heads of the drive faster.  In general, the higher the rpm of the drive, the faster data is accessed or stored on the platter.  Drive vendors normally state the rpms of a drive as part of the name. HP SATA drives currently spin at 5400 or 7200 rpm while HP SAS drives come in 7200, 10,000, or 15,000 rpm speeds.

• Sequential read
• Sequential write
• Random read, or
• Random write

Seek time is the time it takes to move the read/write head to the right place on the platter. Related to seek time is rotational delay or latency: the time required for the addressed area of the disk to rotate to the position where the read/write head can get to it.  The transfer time is the time it takes to actually read or write data from/to the platter. All three of these and spin-up time (the time needed to speed the disk to operating speed )determine the disk access time of a drive.

One other common term used when talking about drive performance is data transfer rate.  This is often measured in bits per second and refers to the average rate data is moved from the drive to the storage controller. Often when people talk about data transfer rate, they are actually talking about system bandwidth or throughput, which is the rate at which data travels from the drive to other components of the server/system.  The throughput of the system depend on the data transfer rates of the drive, the controller, and the system BIOS and chipset – any one of these can be a bottleneck.

So, is rpm the most important measure of drive performance for your application/environment, or do you normally pay more attention to the other measures?