Substitute Disk Qualification Procedure When fulfilling a service spares order, customers may receive a hard disk drive that is different from their original. Substitute devices are necessary as older technology products reach end-of-life and are no longer available on the market. The HP disk Q process consists of sophisticated, vigorous testing to ensure that disk drive substitutions are compatible with customers’ systems. Customers enjoy peace of mind knowing that HP has developed and maintains one of the most disciplined and well-structured testing processes in the industry. With superior qualification and testing. The differences between the original and substituted product may be in spin speed, capacity, interface, or all of these.