docs on storage pools?

So far I've been using files and/or LVM partitions for my VMs -- basically by using virt-manager and modifying existing XML configs and just copying my VM files to be reused. I'm wondering how KVM storage pools work -- at first I thought it was something like KVM's version of LVM where you can

read/write performance degredation in ubuntu/debian?

I have run iozone on my ubuntu 8.10 VM and it says: random randombkwd record stride KB reclen write rewritereadrereadread writeread rewriteread fwrite frewrite fread freread