Different Speeds on 2 Identical Drives?

[khollister]

I have 2 WD Caviar Black drives that are installed in my Mac Pro. Both show the exact same part number in Disk Utility, both are less than half full, both verify fine with Disk Utility. However one shows 125-130 MB/s RW with AJA and the other only delivers 90 MB/s. What gives? Just a sub-standard drive? THey are in adjacent bays in the MP, used as is - nothing changed. They are OEM drives thru Amazon from a few months ago. Both were erased and formatted prior to putting them in the MP a few weeks ago.

Ideas?

 

[khollister]

OK - not sure why, but I solved my own problem. On a hunch (and because I had nothing else to try) I used iDefrag 2 to perform a full defrag of the drive. It appears that for some reason, the back section of the drive was being used instead of the outer, faster section. After defrag, which moved everything to the top (outer) portion of the partition, the RW speeds are almost exactly the same as the other Caviar Black drive installed.