Random access time in RAIDs

The basic characteristics of a data storage speed are:

• access time which is defined as time delay between when a request is addressed to a storage device and the moment the requested data begins to come in. 
• throughput is sustained average transfer rate.

It is well-known that RAID level 0 increases throughput (N times increase ideally). When one plans to build a RAID array, only the throughput numbers are considered, not thinking about access time.

Access time in a regular disk includes the time to position a read head above the track (so called seek time) and the time which is needed a drive to bring a sector under a read head (so called rotational latency). No matter how many member disks are in RAID 0, there always exists such a sector which is simultaneously the furthest away from the head and this sector is not contained in the cache. For this sector the access time will be the same as in case of a single drive. The only way to decrease access time is to stick to an SSD.

P.S. One can easily estimate access time (and other performance characteristics) using free benchmark software BenchMe.