My notices about ATA performance

[Andrey Smagin]

Hi ALL.

I have 2 PC.
1. iP 166 (RAM 48Mb)
2. Duron 1133 (RAM 1Gb)

2 HDD - WD and Seagate  (120GB/8Mb cache).

Kernels used
FreeBSD 4.8 RELEASE
FreeBSD 5.1 RELEASE
FreeBSD 6.0 CURRENT (1-2 week old)

Test speed of copying 1 large (600Mb) file
from 1 HDD to another.

If put HDD's on PC 1 
under 4.8  -  7-10 MBytes/s (UDMA33)(60%CPU Usage)
under 5.1  - 2.7-3 MBytes/s (UDMA33)(100%CPU Usage)
under 6.0  - 2.7-3 MBytes/s (UDMA33)(100%CPU Usage)

If put better CPU K6-2-233 on PC 1 then speed of copying increased 
under 5.1  - 3.2-4 MBytes/s (UDMA33)(100%CPU Usage)
under 6.0  - 3.2-4 MBytes/s (UDMA33)(100%CPU Usage)

If put HDD's on PC 2 
under 4.8 not tested  
under 5.1 - 34-41 MBytes/s (UDMA100)(~30%CPU Usage)
under 6.0 - 33-41 MBytes/s (UDMA100)(~30%CPU Usage)

Why speed of IO operations very depend from CPU power in 5x and 6.x ?