whats the best storage setup for KVM when using direct attached raid? surely using disk image files on a parent ext4/xfs file system isn't the best performance? Should I use host lvm logical volumes as guest vdisks? we're going to be running various database servers in dev/test and wanting at least one or another at a time to really be able to get some serious iops.
Stay away from LVM if you want performance. There is something single threaded in it which stops you from hitting really great performance. qCow2 will work pretty okay but you cant get away from the fact that you are running a filesystem ontop of a filesystem which is never going to be awesome.
In centos, use elrepo and install the "kernel-lt". This will give you a much later kernel which is great for KVM as much improvement has been made from the stock 2.6.32 kernel.
If you need really good I/O then use 10G networking and turn one of the boxes into a ZFS/NFS and put your virtual images on that. My experiments with FreeNAS were extremely potent and quite stable.
Remember that a single SATA harddrive has an approximate equivalent performance of 1G ethernet. 100MB/s or so.
its virt-manager worth using, or is it too simplistic/incomplete ?
Virt-Manager is an ok GUI tool but I would recommend using command line tools virt-install and virsh. They require a little more learning but ultimately give you a better understanding of the stack. They are very powerful when you learn to script with them if you dont have the ability to write python (which I dont)
will virt-manager or some other tool 'unify' management of these 4 VM hosts, or will it be pretty much, me-the-admin keeps track of what vm is on what host and runs the right virt-manager and manages it all fairly manually?
Yes however this is just the creation and destruction of VMs. You cant do live migration because you dont have a shared storage device (unless you use my ZFS NAS idea)
I would stay away from openstack / RHEV (which is actually a fedora project called ovirt) They add a layer of complexity and inflexibility which is not so useful in a lab environment.
Ta,
Andrew
P.S.
Here is a virt-install command that i found in my bash history :)
virt-install --connect qemu:///system -n nfs-server -r 2048 --vcpus=2 --disk path=/vols/nfs-server.img,size=20,device=disk,bus=virtio --vnc --vncport=9922 --vnclisten=192.168.0.11 --noautoconsole --os-type linux --accelerate --network=bridge:br0,mac=00:00:00:00:02:00,model=virtio --hvm --cdrom=/vols/CentOS-6.4-x86_64-minimal.iso
"That may be the easy way, butits not the Cowboy Way"
-- john r pierce 37N 122W somewhere on the middle of the left coast
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