Low RAID5 Performance with 3ware 9650SE Card

[Maverick0984]

The array is currently set up as a 5x750GB RAID5 disc array. Striping is 64KB. These are the performance benchmarks I'm seeing and they scare me. Write cache is enabled, not really sure what the heck else can be going wrong.

The drives are the following:

WD7500AAKS

http://www.newegg.com/Product/Product.aspx?Item=N82E16822136131

Benchmarks are as follows:

http://maverick.poundcs.org/HDTune_STR.jpg
http://maverick.poundcs.org/HDTune_RW.jpg
http://maverick.poundcs.org/HDTach_STR.jpg

For something to compare against, which I imagine should perform worse...here is my RAID1 array built with 2x150GB Raptors.

http://maverick.poundcs.org/HDTune_STR_RAID1.jpg
http://maverick.poundcs.org/HDTune_RW_RAID1.jpg
http://maverick.poundcs.org/HDTach_STR_RAID1.jpg

Any ideas what is wrong? Spent alot of money on the card for it to perform like that :-/ The RAID1 array is setup on the motherboard ICH9R so it is kind of like comparing water to sand...2 different array types and 2 different chipsets, so I understand it isn't so useful to compare.

[Maverick0984]

So, I just noticed the block size change. I changed it to 8MB (the largest) for HD Tune and ran the test with the raid 5 array again and got these results...

http://maverick.poundcs.org/HDTune_STR_8MB.jpg

If that is the only problem, needing to change the block size, does that mean I cannot trust programs like HD Tach since this feature isn't available?