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SQL Server, SANs and Virtualisation Expand / Collapse
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Posted Thursday, January 8, 2009 7:38 AM


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Conan Whalen-McKain (1/8/2009)
I was hoping to recieve from your article a more precise breakdown of how you are making virtualization work. I have been the guy trying to use VMWare server to make it work and just found it to not handle at all well. Could you perhaps discuss more precisely how this works and what the product core is you are using?


I don't want to hijack Perry's discussion on this, but to help him out, can you post what version/edition of VMware you are using, and what your host hardware configuration is? Then the number and type of virtual guest servers you are trying to run on that and their sizes for vCPU, memory, and what software runs on them?

My company has a very large virtual environment, and for SQL my virtualized production servers outnumber my physical ones 4 to 1 and it works great, but the above information is all important to maybe helping provide information about what might be your issues.


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Post #632379
Posted Thursday, January 8, 2009 7:38 AM


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Good article.
I would say VWWare can be used in the testing environment, but not in a production Environment. Especially if you have very busy DB's.


-Roy
Post #632380
Posted Thursday, January 8, 2009 8:02 AM
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In my experience, the benefit of virtualization for SQL server is how much you are willing to trade off improved management for performance.

On the ease of management side, virtualization (VMs with SAN storage) give you ready ability to re-allocate space (disk and physmem) and relocate instances to make better use of hardware with less (or no) downtime.

But depending on the workload, the performance giveup can be huge: as an obvious case, you generally loose the ability to map SQL server partitions to spindles, which will crush performance if your partitions are properly designed. In my company, we have had great results with virtualization for sharepoint and fileserver uses, but my analytics datawarehouse system saw approximately a 10x performance improvement when we eliminated the virtualization (VM and SAN) and ran on the bare metal with the same number of spindles. As we are more than happy to give up some management flexibility for more performance for this application, the bare metal was the way to go.

Which all goes to show that you need to match the solution to the problem.....



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Post #632416
Posted Thursday, January 8, 2009 8:05 AM
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Good article.

Here's a basic question:
How does one verify which physical array the database files and backups are located on in a SAN? I suspect that I have my backups located on the same physical array as the data files and want to separate them. My network admin seems to think this does not matter anyway because according to her, there is only one controller for all the arrays. I always thought there are separate controllers for each array (no single point of failure!). We do not have an in-house SAN admin and I only have a basic understanding of how SANs work.

Thanks!
Post #632420
Posted Thursday, January 8, 2009 8:08 AM
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Currently, I am not engaged in using VMware. I just was trying to use it about 4 years ago. I was hoping to get a better picture of whats needed to really run virtualization and make it successful. The experience of a few years ago did not make me a great fan of virtualization for database servers. I believe this is probably the future as the possible hardware failure immunity and ease of disaster recovery makes this just too good an a possibility to ignore. Also my current company is considering this move and I am looking to give the sound technical advice that I am here for.

Thanks
Post #632424
Posted Thursday, January 8, 2009 8:14 AM


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We use VM's in production quite a bit.

It's a great (cheap) solution for those vendor applications that require SA.
Licensing is an issue for those not on enterprise licensing agreements, but I believe a processor license will allow you to run as many vm's with SQL as you want (on that processor). This probably doesn't apply to the OS license... but I'm not a licensing expert.

Anyone have some insight on this?

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Post #632431
Posted Thursday, January 8, 2009 8:36 AM


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Not to be a forum hog (oink oink),

but something else to consider with SANs and VM's, is that lots of your hardware performance measurements go flying out the window.


for example, say you're on shared disk on the SAN and you're showing 70% Disk utilization. Behind the scenes the apps that are all sharing the SAN disks could be filling the /actual/ available throughput. I've not run into it yet, but it's something I try to keep in mind. Depending on your organization, you might try to get some access to the SAN tools to see the actual disk use on shared disk... or demand dedicated disk.

The same principles apply to virtualization and Memory/CPU measurements.



I'd be interested to know if anyone has the answers.



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Tips for new DBAs: http://www.sqlservercentral.com/articles/Career/64632
My other articles: http://www.sqlservercentral.com/Authors/Articles/Craig_Outcalt/560258
Post #632457
Posted Thursday, January 8, 2009 8:41 AM
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This is a good treatment of a complex subject in a short space. Thanks for putting this together!

It might be useful to compare VMware and Hyper-V from Microsoft, rather than the older 2K5 technology you mentioned. With Hyper-V from Microsoft, SQL Server is now supported, and Hyper-V is far superior to 2K5 in that respect.

Something that is important to keep in mind as well is that it is a bit more of a challenge to cluster SQL Server on any Hyper-V, and without that it is difficult to do rolling upgrades.

- Buck



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Post #632466
Posted Thursday, January 8, 2009 9:02 AM


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Sir Slicendice (1/8/2009)
In my experience, the benefit of virtualization for SQL server is how much you are willing to trade off improved management for performance.

But depending on the workload, the performance giveup can be huge: as an obvious case, you generally loose the ability to map SQL server partitions to spindles, which will crush performance if your partitions are properly designed.


This boils down to implementation and how you have structured your infrastructure early on. The SAN LUNS I have are dedicated to SQL, and at the console level of ESX we can see what the IO being done by that LUN. I have a 300GB data warehouse on VMware that runs just fine, in fact I have less problems from it because it is designed properly than I do from some of our < 2GB databases on physical hardware that have bad designs. One of the < 2GB databases was moved off of VMware because the vendor refused to support it on a virtual machine because that was the problem. Now on a dedicated 2 processor 4GB RAM x64 Physical Server and it still won't perform, and the database is small enough to exist completely in the Buffer Cache.

You can certainly track performance in ESX if you plan your infrastructure properly.


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Post #632495
Posted Thursday, January 8, 2009 9:04 AM
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Licensing for a VM is the same as a physcial machine. If you have 5 VM's installed, you have to license SQL Server 5 times.

Most often the problems people are trying to solve with VM's are far better corrected by using multiple Instances on the same physical system - in this case, the license is as you mentioned.

- Buck



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Post #632497
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