I have problem with some very slow data transfer to my hard drives. Details:
1. Three 250GB IDE drive units set up as a single drive by LVM.
2. Average data transfer rate over several hours from a high-speed SCSI tape drive unit is only about 2.5MB/sec.
3. While the above data transfer is in progress, a top command shows kblockd/0 and kjournald as the only two processes with any significant CPU usage. (kblockd/0 averages about 15-20% and kjournald about 10%)
4. smartctl checks show all three drives are good.
5. The OS (RHEL4) is on a separate IDE hard drive, but all commands run very slowly any time there's a data transfer in progress to the LVM drives. (No noticeable slowdowns at other times.)
6. When a data transfer isn't in progress, an hdparm -t on each of the 250GB drives gets a data rate of about 10MB/sec.

Any ideas for what's behind it or how to improve the data rate?

Thanks!

you didn't mention filesystem used (ntfs is slow!)
-try to boot with single disk setup, so you can see if that is caousing troubles.
-many times, there is a problem with services that do thumbernailing, p2p hashing, and other that requre to got trough many files..

Let me make my last post understandable

Try turning on DMA
hdparm -d1 your_drive

Thanks for the suggestions. No progress yet though...

File system is ext3.
There are very few services running on the system; it's sole job is to make & retrieve backups from tape.


I tried hdparm -d1 but got an error message:
HDIO_SET_DMA failed: Operation not permitted
using_dma = 0 (off)

Ok. It's not loading the correct module for your chipset. I Find it helpful to compile that in instead of generic ata support