Here’s some of the reasons companies usually virtualize their SQL Servers:
- Cost savings on hardware
- Cost savings on Windows OS licensing
- Cost savings on SQL Server licensing
- Protect against the failure of a single hardware element
- Leverage extended features for Disaster Recovery
- Automatic load balancing across multiple hosts
- Easier hardware replacement/migration
When we perform a SQL Critical Care® on a virtualized SQL Server, we often ask, “Are we actually getting those benefits?”
1. Cost savings on hardware – do you find yourself putting one SQL Server guest on each host, isolating them to make sure they get the performance they need? If so, you’re not actually saving money on hardware.
2. Cost savings on Windows OS licensing – as a standard, some companies license all their virtualization hosts with Windows Server Datacenter Edition in order to get unlimited virtualization rights. However, if you’re only running one guest per host (or just a few), then you’re not saving money here either.
3. Cost savings on SQL Server licensing – for this one, you’ve gotta do a little bit harder work. Add up the licensing you’re spending now, and look at what it would take to run similar instances on bare metal hardware. Keep in mind that you can still buy dual-socket, quad-core servers that are insanely powerful (768GB RAM, dozens of SSDs), thereby keeping your SQL licensing lower.
4. Protect against the failure of a single hardware element – on the free versions of most hypervisors, you don’t get automatic failover protection. You can manually start up a guest on another host with some human intervention. Is that enough for the business, or are they assuming it’ll all happen automatically with only a minute or two of downtime – even when you’re not around? Or even worse, do you not have enough hardware horsepower to start up your biggest SQL Server guest somewhere else if its host fails? Or, heaven forbid, are you using local SSDs with virtualization, thereby missing the entire ability to move guests around?
5. Leverage extended features for Disaster Recovery – VMware and Hyper-V have killer features (and third-party app extensions) that make it easy to replicate a guest from one site to another. Are you using those, or have you given up because SQL Server’s data change rates are too high, and your network can’t keep up?
6. Automatic load balancing across multiple hosts – VMware’s Distributed Resource Scheduler (DRS) will automatically shuffle VMs around between hosts based on resource utilization. It’s an amazing way to react to performance issues with less human intervention. You should be using it.
7. Easier hardware replacement/migration – because SQL Server licensing is priced by the CPU core, and it’s super expensive, many shops choose to improve their virtualization host hardware annually. Whenever they need more capacity in their VMware or Hyper-V clusters, they drop in a couple of new hosts, vMotion or LiveMigrate the most expensive per-core guests over to those hosts (thereby taking advantage of today’s faster processors), and then give everybody else the hand-me-downs. It’s easy to do even live during the daytime. However, some shops are still running their SQL Servers on CPUs that might get featured on Antiques Roadshow.
If you’re not leveraging at least some of these virtualization features, and you don’t plan to…then what was the point of virtualizing to begin with? Jump on in – the water’s fine!