[CentOS] kvm cluster w/ c6

Mon Oct 21 09:21:34 UTC 2013
Andrew Holway <andrew.holway at gmail.com>

> 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.




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= --noautoconsole --os-type
linux --accelerate
--network=bridge:br0,mac=00:00:00:00:02:00,model=virtio --hvm

>                                           "That may be the easy way, but
> its not the Cowboy Way"
> --
> john r pierce                                      37N 122W
> somewhere on the middle of the left coast
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos