How smart are RAID controllers when they're under load?
Given a moderate-to-high-end controller and cabinet (i.e. current standard Dell or HP off-the-shelf kit...), RAID 5, 10gb fiber, at least 3/4 utilized space, and lots of small non-sequential with heavy mixed read/write access to files such as would be found on a file or email server...
Practical implementation question: Given the same amount of space, what would be faster, a small number of large, high speed drives (i.e. 4x 1TB 15,000 rpm) or a larger number of smaller, moderate or low speed drives (i.e. 9x 500GB 7200 or 10,000 rpm) drives?
Theoretical question: Do RAID cabinets/controllers know where the head of a drive currently is and the location they need to seek to so that they can assign reads to the drive with the least head-travel distance? Or does it matter?
What other variables come into play with minimizing response time and maximizing throughput with a large numbers of non-sequential small files on a shared storage array? Note that cache doesn't come into play that heavily because of the nature of the data.