Why is disk performance occasionally so slow?

Yousuf Khan wrote:
David Brown wrote:
Task manager only shows you what is hogging the cpu - not what is
hogging the IO resources. While you are doing your copying,
everything else on the system will run like treacle (Windows does not
prioritise IO or memory properly), yet task manager will continue to
show very little cpu use. Junk like antivirus software and windows
indexing, or background defrag utilities, will all be IO (and possibly
memory) bound, not processor limited.


I often see i/o operations being listed as "kernel time" in the Task
Manager performance graph. You do have to turn on the option to "show
kernel times" in Taskman, though. This is basically like Unix's system
vs. user times.


NT's "kernel and user" times are, as you say, basically the same as
"system and user" times in *nix. But IO is different, and don't show up
in either set of times. Some IO operations take a lot of cpu power
(such as directory operations, or small transfers), and thus add to the
kernel (system) times. Others, such as large block reads and writes,
use very little processing power.

"David Brown" wrote in message
...
Yousuf Khan wrote:

I often see i/o operations being listed as "kernel time" in the Task Manager performance graph.
You do have to turn on the option to "show kernel times" in Taskman, though. This is basically
like Unix's system vs. user times.

NT's "kernel and user" times are, as you say, basically the same as "system and user" times in
*nix. But IO is different, and don't show up in either set of times. Some IO operations take a
lot of cpu power (such as directory operations, or small transfers), and thus add to the kernel
(system) times. Others, such as large block reads and writes, use very little processing power.

Bus-mastering IO does not show up as CPU time, but PIO does.
My DVD-ROM went into PIO mode for some reason, and 1/2 of CPU was kernel.

(to fix this problem, delete the IDE channel in DevMgr and rescan devices)