Wednesday, 21 April 2010

Virtualisation – An Introduction

For the last two years or so, in one capacity or another I have been running SQL Server in virtual land and I wanted to start writing some blog posts on the subject .

I thought I would start providing  a definition of virtualisation and then I thought better of it and I decided to leave it for the virtualisation experts, Scott Lowe in his book Mastering VMware VSphere 4 (you can find his blog here) provides a great definition of virtualisation:

“Virtualisation is the abstraction of one computing resource from another computing resource...when most information technology professionals think of Virtualisation , they think of hardware Virtualisation : abstracting the operating system from the underlying hardware upon which it runs and thus enabling multiple operating systems to run simultaneously on the same physical server.”

So the crux of virtualisation is  thus…You have one ( more likely many) relatively powerful server that act as the physical hosts with a hypervisor technology installed and from that setup  you have enough resources to run many virtual' machines (VMs) all sharing the hosts (physical servers) resources.

I assume you are reading this as a SQL Server professional thinking about running SQL Server in a virtual environment. My initial thought about virtualisation was “It might work for small web servers and applications server but it won’t be suitable for my resource hungry SQL Servers.” but I have come around to the idea of virtualisation and I don’t think that anymore.That said it is not necessarily true that virtualisation will suit all SQL Servers so the answer to the question “Should I virtualise  my SQL Servers?” like the answer to most DBA questions  “It depends!” Brent Ozar (Blog|Twitter) has some great articles and posts on his blog about why you should and why you shouldn’t virtualise SQL Server

Why Would You Virtualize SQL Server?

Reasons Why You Shouldn’t Virtualize SQL Server

If you are thinking about or researching running SQL Server on a virtual platform I recommend checking out Brent’s blog as a place to start.

So to the virtualisation software…In truth I have not got down to the nitty gritty of installing and setting up the virtualisation software myself, that has fallen to the sys and SAN admins. My experience has been with VMware’s ESX although Microsoft have a Hypervisor offering in the form of HyperV and XEN also have an open source hypervisor.

The main benefit of virtualising SQL Server, any server for that matter is you can greatly reduce the physical servers in your data centre thus reducing your power consumption and also reduce the heat (and cooling needed) generated by your server farm…which in turn can result in lower costs and reduced carbon foot print. As a DBA you will be concerned about getting the same performance from your virtual servers as your bare metal servers. From my experiences thus far I have got near enough the the same performance from a virtually provisioned server compared to a bare metal box

You also get a lot more flexibility with virtual hardware, servers can be provisioned very quickly at very little cost.

As I have said there are many benefits of virtualisation and some drawbacks its important to consider both sides when making a decision to virtualisation a SQL Server box.

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