[CentOS] OT: Why VM?

Sat May 28 00:10:04 UTC 2011
Ross Walker <rswwalker at gmail.com>

On May 27, 2011, at 5:29 PM, Devin Reade <gdr at gno.org> wrote:

> But taking the other side of the argument, here are two scenarios where
> I *wouldn't* use virtualization (one could certainly enumerate more):
> 1. A production DB server or server cluster.

I actually have really good experience with MSSQL and ESXi. I have 6 big SQL 2005 servers running virtualized and the RDMs actually performed better under ESXi then they did on the bear metal. It really depends on the backend storage, virtualized CPU and memory perform very well.

> 2. I've had services where I needed to maximize uptime.  One option
>   I tried were VMs and being able to move the VM back and forth
>   between hosts.  That might cover hardware failure, but I'd still
>   take outages when I needed to upgrade software in the VM.  Moving
>   to a traditional HA solution on physical hardware means the outages
>   are now measured in seconds instead of minutes, and most of the time
>   are undetectable by the users.
>   I also tried services where the HA nodes are themselves VMs, but
>   was less than impressed with operational stability.

Again I have had good experiences with VMware HA and FT. HA will restart a VM if it fails or if the virtualization host goes down. FT will keep a mirrored copy running and if the primary fails the secondary will take over. I always felt those terms were reversed.

> When CentOS 6 comes out, though, I'll be interested to see how (2)
> behaves when it comes time to do a rolling upgrade from CentOS 5
> (bring a node down, install and reconfigure C6 from scratch, rejoin
> the cluster, have C6 take over the services, then upgrade the other
> node).

I love CentOS but clustering it is a PITA. Virtualization clusters should just work.

> Thank god for test environments.  And backups.