If you're going to backup VMware clients individually via the guest OS, how the backup software vendor prices it is very important.
As I discuss in Backup & Recovery, there are a few different ways to backup a VMWare system. The three main methods are:
Backup at the VMware level by backing up the image files
You need to create a stable image to back up. One way is to shutdown the guest OS and create a snapshot of it. ESX customers can create the snapshot live. The advantage to this method is that it's built-in bare metal recovery for the guest OSs, and it handles backing up applications just fine. The disadvantages are that you have no file-level recovery for the files in the guest OSs, and that all backups are full backups.
Backup at the VMware level using VMware Consolidated Backup
This allows you to mount the filesystem from the Guest OS at the VMware level and back it up at the file level. This gives the advantage of file-level recovery. The disadvantages include no bare-metal recovery (I don't think) and that it's only currently supported for Windows. In addition, the first version of this doesn't support applications like Exchange, SQL Server, and Oracle.
Backup at the guest OS level
With this option, you basically ignore the fact that the different guest OSs are running on a virtual machine, and just back them up like normally. The advantage to this is that it supports full and incremental backups and application backups, and it has pricing advantages that are the point of this blog entry. The disadvantage is that you have no bare metal recovery options.
The point of this blog entry, though, is to mention something that I don't think a lot of people know. If you backup VMware machines at the OS level, major backup programs are starting to not charge you the same as they do for backing up regular machines. The usual pricing mechanism is to charge for once per guest OS type. For example, if you only have Linux running in your virtual machines, you only pay for one client. If you're running both Linux and Windows in your guest machines, you pay for two clients.
Well, that's somethin, isn't it?