What virtual machine software for fail-over and snapshots?

Question

We're looking to virtualize a few machines with the hope that we can:

a) Take "snapshots" of a machine to use as backups

b) Implement a system where if the software/hardware fails, we can quickly and easily load up an recent snapshot on new hardware and replace the failed machine with a new one.

As always, cost is a concern- there's only 3 or 4 servers we're going to do this with, so we don't want to drop $50,000 on this.

I'm confused by all of the different virtual machine offerings. Which one is does what I want, and does it easily?

Answer 1

Hyper-V core is free, but to get what you want you need to purchase System Centre Virtual Machine Manager to do it.

VMWare ESXi is free, but to get what you want you need to purchase vSphere.

Xen is free, but the free version is always one generation behind the paid I believe.

To do what you want with VMWare and ESXi you'll also need shared storage. To do this with Xen you can use DRDB to replicate, but we've done that in the past and performance can suffer vastly.

As DanBig said, as far as the term "snapshots" goes, in the virtual world a snapshot is linked to the VM and if seperated is totally useless, so they're no good for backups. But all of the solutions have their own backup procedures.

To go into more detail, a "snapshot" is simply a point-in-time frozen version of the HDD, where (in layments terms) all changed bytes are linked to seperate sectors, so that both versions can co-exist. If you seperate one from the other, they're useless on their own, they both need to be kept together to be useful. So you can't just copy a snapshot and expect it to work as a backup. However, all hypervisors have their own backup techniques.

A fairly global one is cloning the VM, as they CAN be seperated from their original (unless you create a "linked" clone), but cloning is an IO-expensive operating, whereas snapshots require almost no IO do. Also, depending on the guest OS and if it supports the various hypervisor "tools" you may not be able to clone a machine while it's booted up (Hyper-V is a good example of this).

Answer 2

I will go out and suggest Ganeti. Superb open source that does exactly what you want, has strong support behind it (it's a Google project) and works wonders. I have 100+ being managed by it, some of those with DRBD (disk mirroring) failover/migration.

The interface is command line based but there's a ganeti-web project walking big steps.

Answer 3

From my standpoint there are three real players in the virtualization space:

Microsoft with Hyper-V

VMware with a few different product offerings

Citrix with XEN Server

They all do the same basic things and have the same basic features. Performance is usually pretty comparable in basic setups. Until you start getting into the really high end features theres not a lot of difference.

Other people will probably point you to a lot of different 'nix based options, and those are all probably fine, these three seem to be the leaders in the virtualization space.

Answer 4

openvz can do what you need it to do pretty well and proxmox VE (free) or solusvm (paid) are good options for this and can do snapshots (backups) which are recoverable to other servers as they are basically templates in which you can create fresh servers

proxmox i believe can hot migrate vps's to different hypervisors or possibly even do it automatically in event of failure if you use some sort of shared storage backend too