I hate virtual machines (was I hate NFS)

(Please note that you’ll probably want to read the previous post before this one)

So, I set up a new virtual machine running Fedora rather than CentOS 5.4 and migrated the services over to it. We did see an improvement, but just not enough. I went into the computer room during break, and several students had gray screens for Firefox and OpenOffice.org.

So I’ve switched us back over to the original configuration (running NFS off of the real servers). I have to admit that I’m quite curious as to what the load will be tomorrow when everyone logs in.

Thanks to those who commented on my last post. The general consensus seems to be that this just isn’t the best area to use a virtual machine.

EDIT:

We’ve been running the new system for a few days now and it’s much more responsive. Logins never take longer than 30 seconds, and none of the students are getting gray windows. Load during breaks now ranges from 7 to 20. I’d still love to see a much lower load, but at least we’re back to a reasonably fast system.

I hate NFS

On our network we have about 100 client computers, most of which are running Fedora 11.  We have two real servers running CentOS 5.4, using DRBD to keep the virtual machine data on the two real machines in sync and Red Hat’s cluster tools for starting and stopping the virtual machines.

We have five virtual machines running on the two real machines, only one of which is important to this post, our fileserver.

Under our old configuration, /networld was mounted on one of the real servers, and then shared to our clients using NFS. Our virtual machine, fileserver, then mounted /networld over NFS and shared it using Samba for our few remaining Windows machines (obviously, a non-optimal solution).

Old configuration (click on image for full size)

There were a couple of drawbacks to this configuration:

  1. I had to turn on and off a number of services as the storage clustered service moved from storage-server01 to storage-server02
  2. Samba refused to share a nfs4-mounted /networld, and, when mounted using nfs3, the locking daemon would crash at random intervals (I suspect a race condition as it mainly happened when storage-server0x was under high load).

My solution was to pass the DRBD disks containing /networld to fileserver, and allow fileserver to share /networld using both NFS and Samba, which seemed a far less hacky solution.

Current configuration (click on image for full size)

I knew there would be a slight hit in performance, though I’m using virtio to pass the hard drives to the virtual machine, so I would expect a maximum of 10-15% degradation.

Or not. I don’t have any hard numbers, but once we have a full class logging in, the system slows to a crawl. My guess would be that our Linux clients are running at 12 to 13 of the speed of our old configuration.

The load values on fileserver sit at about 1 during idle times and get pumped all the way up to 20-40 during breaks and computer lessons.

So now I’m stuck. I really don’t want to go back to the old configuration, but I can’t leave the system as slow as it is. I’ve done some NFS tuning based on miscellaneous sites found via Google, and tomorrow will be the big test, but, to be honest, I’m not real hopeful.

(To top it off, I spent three hours Friday after school tracking down this bug after updating fileserver to CentOS 5.4 from 5.3. I’m almost ready to switch fileserver over to Fedora.)