this is a follow-up to a previous question that I asked (Two servers with inconsistent disk speed).

I have a PowerEdge R510 server with a PERC H700 integrated RAID controller (call this Server B) that was built using eight disks with 3Gb/s bandwidth that I was comparing with an almost identical server (call this Server A) that was built using four disks with 6Gb/s bandwidth. Server A had much better I/O rates than Server B.

Once I discovered the difference with the disks, I had Server A rebuilt with faster 6Gbps disks. Unfortunately this resulted in no increase in the performance of the disks. Expecting that there must be some other configuration difference between the servers, we took the 6Gbps disks out of Server A and put them in Server B. This also resulted in no increase in the performance of the disks.

We now have two identical servers built, with the exception that one is built with six 6Gbps disks and the other with eight 3Gbps disks, and the I/O rates of the disks is pretty much identical. This suggests that there is some bottleneck other than the disks, but I cannot understand how Server B originally had better I/O that has subsequently been 'lost'.

Comparative I/O information below, as measured by SQLIO. The same parameters were used for each test. It's not the actual numbers that are significant but rather the variations between systems. In each case D: is a 2 disk RAID 1 volume, and E: is a 4 disk RAID 10 volume (apart from the original Server A, where E: was a 2 disk RAID 0 volume).

Server A (original setup with 6Gpbs disks)

D: Read (MB/s)     63 MB/s
D: Write (MB/s)    170 MB/s
E: Read (MB/s)     68 MB/s
E: Write (MB/s)    320 MB/s

Server B (original setup with 3Gpbs disks)

D: Read (MB/s)     52 MB/s
D: Write (MB/s)    88 MB/s
E: Read (MB/s)     112 MB/s
E: Write (MB/s)    130 MB/s

Server A (new setup with 3Gpbs disks)

D: Read (MB/s)     55 MB/s
D: Write (MB/s)    85 MB/s
E: Read (MB/s)     67 MB/s
E: Write (MB/s)    180 MB/s

Server B (new setup with 6Gpbs disks)

D: Read (MB/s)     61 MB/s
D: Write (MB/s)    95 MB/s
E: Read (MB/s)     69 MB/s
E: Write (MB/s)    180 MB/s

Can anybody suggest any ideas what is going on here?

The drives in use are as follows:

• Dell Seagate F617N ST3300657SS 300GB 15K RPM SAS
• Dell Hitachi HUS156030VLS600 300GB 3.5 inch 15000rpm 6GB SAS
• Hitachi Hus153030vls300 300GB Server SAS
• Dell ST3146855SS Seagate 3.5 inch 146GB 15K SAS