Slow WD20EARS in RAID5


I’ve looked through a number of forums (including this one) but have been unable to find anything that exactly matches my symptoms, and all my attempts to increase the speed of the drives have failed.


I have 3x WD20EARS-00MVWB0 in RAID5 (onboard ICH10 controller) set up with 2 partitions (1x 500GB, 1x 3.15TB). The array was set with 64K block size, and each partition was formatted as NTFS with “Default” block size. My OS is Windows 7 64-bit.


When I start copying a file from another (local) drive to this array, the speed is very fast (110-120MB/s) for roughly the first 10-12 seconds, and then it drops off completely to a fraction of the speed (4-6MB/s)

[Edit] Also, at random times during the transfer it will sometimes jump to 20-30MB/s for (up to) 30 seconds, and then will drop back down to 4-6MB/s [/Edit]

I have tried:

  • deleting and re-creating the partitions

  • reformatting the partitions

  • defragmenting with Windows Disk Defragmenter

I’m completely stumped =/. Any suggestions would be much appreciated.

I’ve disabled idling with wdidle3, which has slightly increased the low write speed (10-12MB/s instead of 4-6MB/s), but that’s still really slow. I’ve done more searching and tried everything that I could find, but nothing helps.

Please let me know if you have a suggestion for me to try. If I can’t figure this out by the end of tomorrow, I’m going to have to take these 3 drives back to the store =(

Well, the desktop drives aren’t tested/intended for use in RAID5… if you want an enterprise array to work correctly, you’d need enterprise drives, I’d guess.

Do you have a discrete raid card HBA (like LSI, Adaptec, etc) with an onboard procesor for computing the parity data and managing the array [aka -real- hardware raid] ?

No, you do use the “raid function” of the motherboard [aka fakeraid or firmware raid] , so the computation of parity data is done by the host cpu, it is very similar to software raid. (managed by firmware on boot and then by the os [win] when booted.

For a performant RAID5, either you have a Storage Array or a decent RAID HBA for RAID5 and Enterprise Disks.

You can use your RAID5, but do not expect to write fast to it, in fact raid5 it is not recomended for a high write percentage. Use it for saving space for archiving, copy the stuff, then read it.