High loads when writting to LVM

I have a system that I am testing out lvm on to get a feeling about stability and performance. Stability right now seems good, but I am a little worried about the performance currently I am writing out a large file ~1TB using dd if=/dev/zero of=test bs=1M and am noticing the load seams extreamly high "5.21, 5.26, 5.17". Most of the work is being done in dd but I also notice that kswapd0 is also working fairly heavily. Is this to be expected with LVM or do i have things setup wrong. Write performance seems to be around 100MB/s on an XFS filesystem.

System:
Opteron 242 1.4Ghz
2 GB RAM
Tyan S2882
3W-9000-12 in raid-5 with one hot spare
12 Seagate 250MB SATA drives
Fedora Core 2
Kernel 2.6.8-1.521

Judd Tracy
[email protected]

This may be a result of how load average is calculated. What is the CPU usage when doing these (see top)? On a machine with a large number of processes accessing the disk, it is quite easy for a single, I/O intensive application (such as your dd) to drive the load up.

The load average is telling you that you have 5 processes blocked waiting for I/O. Without the dd, the time taken to service each is reduced, and the average number blocked at any given time is therefore lower.

On our combined shell/web/email server, an I/O intensive process will result in a load of well over 10, yet responsiveness of the system is not actually that bad, and cpu usage remains low.

Paul