> > However I did notice a strange thing:
> > for various reasons on both systems I tested,, the copy goes from/to
> > a different disk than the system disk. While I do the copy,
>
> OK, I newfs an old linux partition (which doesn't boot any more anyway).
> doing a cp on the same disk as the system disk freeze X until the
> cp is done.  Same result if I use dd instead of cp.

yes EXACTLY that!
maybe not complete freeze but up to 10s delays. on your machine with i
think faster IDE bus it may be worse.


> Either reading or writing a large file cause this problem (dd if=file
> of=/dev/null, or dd if=/dev/zero of=file)


i often do dd if=/dev/rcd0d of=file bs=2k to take CD image

in 1.5.2 i was normally using machine while doing it. now i can't.

>
> Has anyone idea of what is causing this ?
> I suspect it could be disksort, which cause a single request to one end of
> the disk be delayed to group dozen of requests on the other end of the disk.

if so - apps that doesn't use disk at all for sure (like text editor)
should work fine. but it isn't - delays are small but noticable (up to 1
second).