[CentOS] Disk Activity Monitor

[Dag Wieers]

On Mon, 13 Feb 2006, James Pifer wrote:

> I have a USB disk connected to a Poweredge server. The USB Disk is a Mad
> Dog MegaVault with a 160GB drive installed. It's all working fine, but
> the external LED on the unit is not working. 
> 
> I'm currently running a script (yum-pull) for setting up a yum mirror
> and it sits for long periods of time seemingly doing nothing. I started
> the script this morning at 6:20 for my FC4 yum mirror and it's now 8:50
> and it's still running. A "top" shows very little activity from a CPU
> perspective. 
> 
> The guy who wrote the script says there's probably tons of disk activity
> going on. The script does continue to run because it will eventually
> finish. One might think the slowness is because it's a USB drive, but I
> can copy large amounts of data and do permission changes on files, at
> the same time this script is running, and it all happens quickly. 
> 
> Guess I'm just trying to verify whether there really is a lot of disk
> activity going on. I tried looking at ksysguard, but wasn't very
> successful at seeing what I wanted. 
> 
> I'm not sure I want to use yum-pull if it take 3 hours to run per
> mirror. Right now I'm mirroring FC4, but I also want to do Centos 4.0
> and 4.2, and maybe even Suse 9.2. 
> 
> Are there any other disk activity monitors I should try? 

You may want to look at dstat. With:

	dstat -cd -f

You can compare the output from your CPU (check iowait) and the disks.

Also, beware that the disk i/o is relative to what your disk can handle, 
so there is not clear upper boundary. Graphs may trick you into showing 
how much free disk bandwidth there is, but that is deceptive.

With:

	hdparm -tT

you can check to see what your disk is capable of. And that might help 
interpreting raw values much better. (together with the iowait values)

Kind regards,
--   dag wieers,  dag at wieers.com,  http://dag.wieers.com/   --
[all I want is a warm bed and a kind word and unlimited power]