VMworld Europe 2008 Coverage

What about Virtualized Databases?

In a very interesting session led by VMware's Richard McDougall, we were provided with some insight on running databases in virtualized environments. The session mainly involved Oracle, but according to McDougall, they've found the pointers discussed apply to any database system. Right from the start, McDougall did away with some of the most common performance myths and misconceptions, and listed quite a few positives to the use of ESX and Virtual Infrastructure, paired with databases.

When thinking about virtualized databases, many believe them to be too IO intensive to run efficiently, and as such provide too much overhead. While these concerns are definitely justified, VMware strongly believes that ESX's strong IO subsystem can handle any database satisfactorily and provide a large amount of extra possibilities that should be enough to convince any database analyst to at least try it.

Making use of a single system to run several databases can be quite a fragile setup, and putting platform-specific high availability systems in place can be a costly endeavor. It's for this reason that VMware's "one system fits all" solution might prove very interesting. Apart from the possibility of using VMotion, Dynamic Resource Scheduling, and VMware HA on the systems, there's the option to easily provide powerful isolation, without the need to buy a new system for every database.

For optimal performance on a virtualized platform, VMware offers the following tuning recommendations:

• Always use a 64-bit database
  
• Try to assign enough memory to the VM to cache the entire database and reduce the amount of IO
  
• Make use of Direct-IO uncached pass-through capabilities and Asynchronous I/O (if possible)
  
• Use large MMU pages
  
• Most importantly, optimize the actual storage layout (such as the number of disk spindles). This will have the largest impact.
  
• For Oracle, the log files should be put on the very fastest piece of storage available, preferably dedicated to this task.

At this point, we have not been able to do any actual tests on a setup like this in our lab, but we'll be sure to share our experiences with it once we get around to it. More information on VMware's performance testing can be found at their blog: VROOM!