Chan Chung Hang Christopher wrote: > Complete bollocks. The bottleneck is not the drives themselves as > whether it is SATA/PATA disk drive performance has not changed much > which is why 15k RPM disks are still king. The bottleneck is the bus be > it PCI-X or PCIe 16x/8x/4x or at least the latencies involved due to bus > traffic. In most cases the bottleneck is the drives themselves, there is only so many I/O requests per second a drive can handle. Most workloads are random, rather than sequential, so the amount of data you can pull from a particular drive can be very low depending on what your workload is. Taking a random drive from my storage array(which evenly distributes I/O across every spindle in the system), a 7200RPM SATA-II disk, over the past month has averaged: Read IOPS: 24 Write IOPS: 10 Read KBytes/second: 861 Write KBytes/second: 468 Read I/O size: 37 kB Write I/O size: 50 kB Read Service time: 23 milliseconds Write Service time: 47 milliseconds Averaging the I/O size out to 43.5kB, that means this disk can sustain roughly 3,915 kilobytes per second(assuming 90 IOPS for a 7200RPM SATA disk), though the service times would likely be unacceptably high for any sort of real time application. Lower the I/O size and you can get better response times, though you'll get less data through the drive at the same time. On my previously lower end storage array that I had at my last company a 47 millisecond sustained write service time would of meant outage in the databases, this newer higher end array is much better at optimizing I/O than the lower end box was. With 40 drives in a drive enclosure connected currently via 2x4Gbps (active/active) fiber channel point to point link, that means the shelf of drives can run up to roughly 150MB/second out of the 1024MB/second available to it on the link. System is upgradable to 4x4Gbps (active/active) point to point fiber channel links per drive enclosure, I can use SATA, 10k FC, or 15k FC in the drive cages, though I determined that SATA would be more than enough for our needs. The array controllers have a tested limit of about 1.6 gigabytes/second of throughput to the disks(and corresponding throughput to the hosts), or 160,000 I/O requests per second to the disks with 4 controllers(4 high performance ASICs for data movement and 16 Xeon CPU cores for everything else). Fortunately the large caches(12GB per controller, mirrored with another controller) on the array buffer the higher response times on the disks resulting in host response times of around 20 milliseconds for reads, and 0-5 milliseconds for writes, which by most measures is excellent. nate