Hi,

I get really bad performance during disk transfers (reading a big file, for example), 'top' says the following about my CPU:

Cpu(s): 6.3% us, 21.3% sy, 0.0% ni, 0.0% id, 71.7% wa, 0.3% hi, 0.3% si

I did a little research on what 'wa' is supposed to be and it seems that it means the system's waiting for I/O data to arrive. Does anyone know why my CPU would spend so much time waiting and doing nothing?

According to hdparm, DMA is enabled for all my drives, they run in udma5 mode. The data transfer speed is okay (20MB/sec) and it gets much worse when I disable dma, so this doesn't seem to be the issue. There is enough free RAM available too (> 200 MB, which is all used for file cache). The system isn't swapping either.

My hardware:
Athlon XP 2000+ on a Via KT333 chipset
512MB RAM
Kernel 2.6.9
IDE drives are to Seagate Barracuda IV 80GBs


Any clues?

Nobody got a clue? :-(

One problem is Seagate hard drives uses more CPU power than IBM/Hitachi and Western Digital even though DMA is used. Another problem is it could be your kernel parameters. Use sysctl to tweak the settings of the kernel so that it can cache and buffer data better.

How big of a file are you talking about? If it is something like 4 GB, you may want to use XFS.

Also try to turn off the advance power management for your drives. Print what "hdparm -v /dev/hd[a-z]".