Very slow file transfer with 750GB hard disk

Hi.

Has anyone experienced problem with 750GB hard disk?

I had made my system with 8 x 400GB seagate hard disks without specific problem.
But after I changed my disks with Seagate 750GB, the file transfer rate was fluctuating
and sometimes transferring itself stopped for a short period.

I searched internet and found that there may be some problem on Seagate 750GB with AAK firmware and my disks had that firmware.
I changed the disks again with Western Digital 750GB 7500AAKS but still have problems
in file transferring.

May I have some suggestion?

Thank you.

My disks are arrayed as Raid6.
I tried Raid50 but still got very very slow file transfer rate.

What is the RAID controller and did you setup for performence to use cache. Also check the Firmware version of the RAID controller as well to see if it is up to date.

The situation is that on the same card, same settings, same firmware and same operating environment,
400GB disks do not matter but 750GB disks make problem.

My raid card is 3ware 9650SE with 16 port.
I used Raid50 with 8 disks of Seagate 400GB.
I did not use write back cache because I had not BBU.
The firmware of 9650SE is up-to-dated.
Open-e DSS version is 1.30 and I tried 1.32 and another beta version.
Only with 750GB disks whether Seagate or Western Digital,
I have very very low file transfer rate with Raid6 or Raid50.
The worst rate is 3M/sec and there is hanging at the end of each file's transferring.

I just tried Raid0 with 2 x 750GB disks and It's transfer rate is 35MB/sec.
The process of file transfer is smooth and there is no hanging at the end of each file's transferring.

What may be the cause of bad transfer rate?

With Raid 0, 1 there is no problem.
But with Raid 5, 6, 50 there is slow file transfer problem.

Oops!

After I turned on the write back cache, the transfer rate came to normal.

I'm sorry to have bothered you.

Thank you all.

Thanks for the update :)