How the UNIX system Load Avarage is calculated on Mac OS X and Linux

The Load Avarage values that are shown using the ‘top’ commad or the ‘uptime’ command represent the number of blocking processes in the run queue averaged over a certain time period.

An example fo HIGH Load Avarage:

 load average: 12.54, 12.71, 12.19

these values represent CPU, Disk I/O and Network I/O.

if you run the ‘top’ utility you can seek for the CPU usage and for the CPU I/O waiting time that are represented by the ‘us‘ and ‘wa‘ abbriaviations.

If these uage is permanently around 100% then chances are the problem is related to your CPU.

If the I/O waiting time is mostly above the 80% it means that there could be some problem with the I/O devices suche network cards or failing hard drives.

In my spefic case I notices that in ReadyNAS with 6 disks in RAIDX-2 the load avarage is constatly over 10.00,10.00,10.00. I believe this is normal considering that the ‘md’ process has to keep the RAID chain continuosly checksummed and alligned.

This information has been sources from Andy Millar’s really nice blog I have found digging around: http://www.andymillar.co.uk/blog/2006/12/24/linux-load-average-explained/

 

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About marcomc

Marco M.C. is a System Administrator with 10 years of professional experience in ICT. He has deep knowledge of Mac OS X, Windows, and GNU/Linux. His hobbies vary from DIY, Traveling, learning foreign languages and especially he love to cook and experiment with food from all around the world.
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