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SQL Server on a virtual server


SQL Server on a virtual server

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Majid-454469
Majid-454469
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Hi,

I'm collecting information, recommendations about advantages and disadvantages of usage a virtual server for a SQL Server in production environment.
Do you any test results or benchmarks regarding performance, security, availability and so on?

Thanks
Steve Jones
Steve Jones
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I haven't seen any, but I'm looking for some.

There is one from VMWare, but since they're selling virtual software, not sure how much to trust it:

http://www.vmware.com/files/pdf/SQLServerWorkloads.pdf

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Linda Johanning
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I don't recommend a VMWare instance for a production SQL Server. A virtual machine only gets a portion of disk space, memory, and CPU so performance isn't very good. We had a SQL Server test environment set up and performance was such an issue that it is no longer used. I think virtual instances might be ok for testing functionality only, but I would never use it in production.



Donald Denney
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That's a bit of a generalization, and not really accurate anymore. Virtualization has improved considerably recently, and many production databases perform quite well on a virtual machine.

So the answer is really, it depends on the production database. What are it's requirements for I/O throughput, CPU usage, etc. There are some advantages to using Virtualizaton and also some disadvantages.

If you use pass through storage with a dedicated HBA, the only real tricky part that I have found is the allocation of CPU resources. That's the one part of VMWare that still in my opinion still has some issues that can make performance tuning tricky.

There is a very useful white paper on SQL Server Consolidation, and this includes using Virtualization to consolidate.

Here is the information about the paper:

Consolidation Using SQL Server 2008
SQL Server Technical Article

Writer: Allan Hirt, Megahirtz LLC (allan@sqlha.com)

Technical Reviewers: Lindsey Allen, Madhan Arumugam, Ben DeBow, Sung Hsueh, Rebecca Laszlo, Claude Lorenson, Prem Mehra, Mark Pohto, Sambit Samal, and Buck Woody
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We have about half of our production SQL servers on VMWare. For the most part these are systems that are not highly transactional. I've really had no issues with them over the past couple of years. In the beginning we did have to be careful about which applications shared the same VM host. Things also got better when we began to use SAN as the disk storage medium.

One really nice plus is the ability to clone the VM to create a Dev or Test environment.



GTR
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I agree with Linda, we have SQL instances on Virtuals in Test Environment for more than two years. We had problems with Virtuals Host failing which brings down all viruals hosted on that server. I wouldn't recommend using Virtuals in Production environment, no chance.

EnjoY!
Joie Andrew
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I agree with Donald Denney on this. I went to an England PASS meeting on this two years ago, and the answer was "it depends". The biggest issue with virtualization tends to be capacity planning. If the physical box is configured correctly and the SQL server being virtualized does not have demands that will bring other VMs on the box down, then I believe it can be done safely. Not only that, but for things like SSRS and configuration databases that do not change much, it is probably a good solution for them.

On the other side of the coin though, I do not think that mission critical databases should go on them. There is a lot that I have read about the features of virtualization, but a lot of it has been stated without real-world data, so that leads me to believe they are selling proof-in-concept solutions, which I do not want to risk with my critical data. Also, some features such as virtualization snapshots are not supported by Microsoft under any vendor, including MS. I also do not think that it would be able to handle a replicated environment well either.

The choice is yours, but I tend to think of mission critical heavy OLTP instances as the last ones to be virtualized, if at all.

Joie Andrew
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Donald Denney
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I'm not a Windows Administrator, so I don't know all of the details or pitfalls related to making VM stable. I do know that we have very little problem with our Virtual Machines staying up or being stable.

Partly that might have to do with a product called "VMotion", which not only can be used to migrate Virtual Machines to other Physical "ESX" frames, but will automatically fail those machine over to other frames in the result of failure.

I've seen where an ESX frame went down, and the Virtual Machines on there migrated to several other frames, with VMotion deciding where they should go based on resource availability and resource needs, and the people using the Virtual Machines had no idea they had even migrated. There is some performance degradation while this happens, but it's much more seamless that failover within a Microsoft Cluster.

Not only does the database instance not shutdown, but the windows OS never "shuts down". It's pretty impressive.

I do have misgivings about he ability of the VM environment to provide truly reliable, consistent resources without adversely impacting performance. For that reason, I too am leery of putting anything too mission critical or performance sensitive on them, especially something that is truly resource intensive.

I started out being a pretty big VM sceptic myself to be honest, but over time I've been shown that a lot of my original fears unfounded.
Michael Valentine Jones
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We have about 50 SQL Servers on VMs, mostly production, but some are development. We do not generally put highly loaded servers on VMs, but they are great for "one off" special purpose servers.

I would say that as long as the VM environment is well managed, that there is no problem. In general, our VM servers have no more downtime than "real" servers.

It saves a lot of management effort and money to be able to do physical to virtual migrations for older servers, rather than keeping them on hardware maintenance contracts or replacing them with new hardware. Being able to move from older, failing hardware without having to reinstall OS, SQL,and application software is a huge time saver, especially when it is older software that is not well supported.
paul.aasmundstad
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Multi-instancing is IMHO a superior approach. You get hardware and licensing consolidation, streamlined patch/sp processes, a true picture of hardware level metrics, and a better optimization routine for parallel or heavy loads. Unless you NEED distinct operating environments, there is no reason to pursue VM vs. multi-instancing. Since we don't like to share IO or other resources with other kinds of servers, are mindful of HBA limits, and want "true" resource pictures for performance tuning and capacity planning, we'd prefer to not to go down that route. Ideas of using host migration for SQL servers to me is not good - if you are improperly balanced at the ESX level, this technology covers up your more fundamental design problem. Sometimes SQL servers will have heavy load (indexing, jobs, etc) - I don't want that to overload my host, and if I do, I want more resources permanently, not temporarily by moving the server. Otherwise you end up with round robin server migrations instead of solving the problem.

VM is a great way to sell SAN storage, save rack space, get more utilization out of unver-used resources, and cover up capacity/performance planning mistakes. None of which have anything to do with what I am concerned with as a DBA. However, I think you'll find multi-instancing meets the consolidation and cost saving goals of VM, but in a way that keeps performance, manageability, and responsibility in the hands of the DBA.
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