So the problem starts off when I realize that Diskpart and Disk Management are showing me a drive order wholly different than the physical layout attached to the SATA ports.
The WD Black is physically on SATA 0.
The M4 is physically on SATA 1.
Inside the BIOS configuration the above listed order is confirmed. As the above picture illustrates, Windows is reporting an inverse value. SATA 1 has become Disk 0 and SATA 0 has become Disk 1.
A quick check of my laptop (ICH8 vs the ICH10) shows an identical behavior. The physical SATA port layout and the disk enumeration per Windows don't match. Not serious, not even problematic, but it tweaks at the OCD monster in me.
Lo and behold this behavior is apparently so common that it warranted a KnowledgeBase
So I proceed to dig a little deeper into the configuration of the disk array in Device Manager and find that the corresponding SATA ports also have wholly incorrect DMA/throughput values.
SATA 0 is reporting that it is running in Multi-word DMA 2. A very old DMA mode that is limited to 16.6MB/s.
SATA 1 is reporting that it is running in PIO 4. The checkmark used to enable DMA on the device in Windows is cleared. PIO 4 has a throughput of 16.6MB/s, but unlike MW-DMA dumps all the I/O work onto the CPU.
The system has felt responsive, but at this point I'm figuring I must be blind. As the results being reported imply that disk performance is in ruins.
I try applying the checkmark. The mark fills the box and hitting okay closes out the dialog, but upon opening the applet again I see the checkbox is once again cleared. I try uninstalling both the SATA controller and the disk drive, rebooting, and letting WIndows detect hardware once again. I return to Device Manager only to find the checkbox still cleared and PIO 4 still reported.
Thing is I really should be feeling the fact that my C: drive is in PIO. The boot process and the overall interaction with the system is just entirely too smooth for the sort of performance degredation that should be happening.
So I decide to benchmark the situation.
Yeah. Not MW-DMA 2 and not PIO 4. So is it Windows or the Firmware?
Off to Google where I find I'm not alone
in experiencing this behavior. It appears on other brand motherboards and operating systems. Using higher numbered ports (e.g. SATA 3) makes the problem entirely disappear. I'm guessing the storage controller firmware in the ICH is responsible for this entertaining quirk.
1. Being meticulous about which SATA ports you plug your drives into won't pan out like you think.
2. You can't trust the DMA status reported by Windows.
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