On Tue, Jul 7, 2009 at 4:38 PM, Holger Parplies<wbppc AT parplies DOT de> wrote:
> No, my point was, the "load average" is an attempt to fit the state of a
> system into one single number (which, as we've agreed, is only good for
> getting a quick impression, nothing more).

Exactly.  On Linux systems (don't have enough high performance
experience with other systems to say conclusively) the load average
simply gives you a rough indication of the number of processes that
are in the run queue.

If you have one process running using 100% CPU, your load average will be 1.

If you have one process running waiting 100% IO, your load average will be 1.

To get a full picture you can run top (make sure if you have multiple
CPUs you expand the display to show each one) or vmstat (I typically
use `vmstat 1` to watch the data on 1 second intervals).

vmstat has the benefit of splitting out the number of processing
running on CPU and waiting on disk (see the first columns r and b) as
well as showing you overall IO load and the type of CPU utilization.

Here's a sample from vmstat of my desktop/server system running a
local and remote backup at the same time:

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 2  2      0  35592 200332 1459116    0    0 73100   392 2884 2375 65
12  0 24  0
 3  2      0  21508 200648 1473972    0    0 55036     0 2523 2641 28
6  4 63  0
 2  1      0  24940 201092 1471664    0    0 81664     0 3085 2949 33
9  1 58  0
 1  2      0  25512 201376 1472784    0    0 81216  1064 3094 2883 28
8  0 65  0
 3  1      0  23612 201732 1475760    0    0 81256     0 3039 2939 28
8  1 64  0

Here we can see a pretty good mix of CPU and IO wait - Improving the
capacity of either would lead to a reduction in backup times.

-Dave

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