Q: How do you determine what type of drives to use for a customer?
It all comes down to performance requirements. There are tools that can be used, such as perfmon in Windows and sysstat or iostat in various flavors of UNIX, that can help you determine the IO rates for a particular environment. Next, make sure that for the given capacity, you have allocated enough spindles to meet the customer's performance requirements. A typical rule of thumb is that FC or SAS drives at 15,000 RPM can handle 180 IOPS while a 10,000 RPM drive can handle 120 IOPS. If you're concerned about performance at all, don't use SATA; that's the drive to use for archive and for applications where performance and reliability is not a concern. It's also worth noting that if performance is the customer's only concern, flash drives are starting to become available in high-end enterprise arrays. While they are expensive, nothing can come close to competing with them in terms of performance.