I've been struggling with this for several days. I started this thread over at hddguru.com if you want some background on some troubleshooting that I've tried, but here's the basics:

Fresh install of Win7 SP1 64 bit to 256GB Samsung 850 Pro
Two 750 GB WD7500AYYS in a RAID 0 controlled by onboard Intel P55 RAID controller
Asus P7P55D-E PRO motherboard
BIOS 1703 (latest from ASUS' website)
Intel RST 13.2.4.1000

BIOS is set to RAID
DVD drive and 3 TB are also on the Intel SATA ports

The write performance on the RAID is abysmal, rarely breaking 5 MB/s.

<edit, updated screenshot>
Screenshot from ATTO:
https://www.dropbox.com/s/g1pbeahhpausz3....54.30.png?dl=0

What am I missing?

Thanks, I'll give that a shot. I've been reading carefully through the guide, but not sure where to find the 11.2.0.1006 driver. I found and downloaded the v11.2.0.1527 oROM, but didn't see any links for drivers, or maybe I'm misinterpreting something.

Just for my own information, is this referring to Intel RST v11.2.0.1006?

RAID oROM and driver are now running at the versions noted. Still the same behavior. Any other ideas? After all the work I've gone through, I'm beginning to wonder if there is a problem with one or both of the RAID drives themselves?

Did you check the smart status of the RAID0 disks? CrystalDislInfo (http://crystalmark.info/redirect.php?pro...stalDiskInfoX64) can show this for disks that are part of a raid system.

Update:

I broke the RAID apart and ran SMART and ATTO read/write tests on each disk, with the results below. One of the drives has a clean SMART report, but mimics the poor write performance of the RAID:

Good WD7500AYYS disk:
ATTO report:
https://www.dropbox.com/s/w8g28mx44bv78c....29.50.png?dl=0
SMART report:
https://www.dropbox.com/s/jeubvhrzc23jm2....55.48.png?dl=0

Bad WD7500AYYS disk:
ATTO report:
https://www.dropbox.com/s/03781h7vznkqyb....00.28.png?dl=0
SMART report:
https://www.dropbox.com/s/lcdc17sa1ygkoh....54.12.png?dl=0

The ATTO results from the bad disk look just like the results when they were RAIDed together, so it's definitely holding things back.

Recommendations on what I should try before replacing the bad drive? CHKDSK, or something else?

Well, running CHKDSK marks the bad sectors as unusable, which would help for the moment. You could also run the WD Data Lifeguard Diagnostic Tool, which can be found here: http://support.wdc.com/product/download....0&sid=3&lang=en

But having this Reallocated Error means, this drive is slowly dying. I would replace it at soon as possible.

Solved! Bought two new 1 GB WD Reds and did a RAID 0 on 'em. MUCH better write performance. Thanks for all the input, I learned a lot. Happy Holidays to all.

https://www.dropbox.com/s/2flwpfia3182dg....20.47.png?dl=0