Linux I/O scheduling - ionice & co

[devzero]

Hello experts!

Whenever I do large file operations on my VMware GSX Server (copying/backup operations on the HOST), all the VMs become dead slow, regardless what elevator i select at boot time.
 
what can I do that dedicated processes get higher preference regarding I/O ?
 
from this list i found, that in recent kernels we have cfq/ionice for this.
is this rated "stable" and does it already work well?
 
maybe there are alternative approaches for this?
 
let me give another example:
 
if i start an I/O hog like "dd if=/dev/zero of=test.dat" the whole interactivity of a linux system is being influenced very negatively. i have found that working on a system running an I/O hog often becomes a real pain.
if i start an CPU hog or syscall hog like "while true;do true;done" or "while /bin/true;do /bin/true;done" this never has such bad effects than starting an I/O hog.
 
is it possible to adress this by some more "fine-tuning" or is this just because of the "nature" of I/O scheduling ?
 
i would be happy if somebody could give a comment or share his experience about this.
 
TIA
roland k.
systems engineer
 
ps:
no comment about the behaviour of a windows system which is under high I/O load..... ;)
 
 
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