OS X Technologies :: Unix Processes Go To Sleep Before Completing

I  regularly run unix commands remotely, or on network-attached drives - exampels are rsync; rm (-r) etc. 

For the following assume its on a NAS drive, mounted to 'Volumes/drive" 

On large jobs, i find that these processes do two things that i cant explain, nor do i like: 

1. they seem to sorta slow down and stall occasionally. I knwo that's vague

2. they stop running when the computer goes to sleep 

Now, the real questyion is, since an active proces is underway, why did it go to sleep? 

I do have "wake on network activity" checked. 

I was able to mostly eliminate this problem by turning off "sleep after X minutes" and moving the energy saver slider to "never" 

Info:
MacBook Pro (15-inch 2.53 GHz), Mac OS X (10.6.8)