Last Updated 19/Feb/2009
Slow System? It could be the Hard Drive!
Iain Laskey has a quick check and fix for some slow system problems
We recently built and set up a Windows Home Server system which so far has worked reasonably well. However, when the client PCs were backing up, the WHS machine seemed very CPU bound - often at 98-100%. The CPU isn't great - an Athlon XP 1800 but it's also more than adequate in theory for the job in hand.
We recently had a slight hiccup when opening up the machine for some tweaking whereby a drive cable had got disturbed and the drive initially disappeared, then returned but with a corrupted name in the BIOS and after some further cable reseating, came back properly. Somewhere amongst all this, the number of drive errors no doubt being generated had caused WHS to decide to give up on using UDMA to communicate with that drive - by far the preferred option as it's low on system resources and fast - and instead reverted to PIO mode.
UDMA uses direct memory access to copy data from the drive straight into memory without bothering the CPU much. PIO on the other hand uses the CPU for each and every byte of data going to and from the drive. It was this that was killing the system.
The fix is to go into the control panel, select 'System' and then the 'Hardware' then 'Device Manager' . Here you can see all the components in your PC. Select your drive controller and examine the mode it is using. You should be able to change it back. If not, your problem is a bit deeper and beyond this quick fix.
Assuming you can change it, reboot and hopefully you'll have a far sprightlier system. The Windows Home Server box now uses around 2-5% CPU when backing up and moving files - a huge improvement and a much snappier system response all round.
This problem isn't always caused by cable or drive problems, sometimes Windows just gives up on a UDMA mode and reverts to PIO for no obvious reason and it's not just WHS either - all versions can do this. We've certainly seen it happen on XP several times.
It's also worth checking the settings after a few days to ensure they've stuck in case there is a genuine problem and it's reverted back.
In a nutshell, if your system seems to be using vast amounts of CPU when doing what should be very little, it's well worth checking for PIO mode in the drive controller.
