Virtualization

EMC World 2008 Day 1 (The first post)

While waiting for the first keynote to start I figured that this would be as good a time as any to write a quick post.

 I just got out of the first session of the morning.  I decided to catch the VMware VI3 session which went over the new features of ESX 3.5.

 It was a very good session packed with great info about the new features of VMware ESX 3.5 which came out a few months ago.

3.5 introduces the Storage Vmotion.  It’s similar to the regular Vmotion which moves VMs from one host to another, but it’s designed to move a VMs storage from one disk (LUN, array, etc) to another disk within the same host without taking the VM down.  In prior versions of VMware to move a VM from on disk to another you would need to power the machine down and then move the machine.  It can now be done as a live operation.  It does temporally double the memory and CPU requirements of the guest OS, and it is a CPU and disk intensive operation and should be done off hours, but it’s a great way to move from a full disk to an empty one.

 Another great technology which I was introduced to is the VDM or Virtual Desktop Manager.  As I understand this technology it allows you to take a single Windows XP guest OS, and allow many people to connect to it.  The VDM places a connect pool in front of the Windows XP guest OS and as people connect to it, it takes a snap of the guest OS, and lets the new user use the snap.  This allows many people to use a single Virtual Machine without increasing the amount of disk space required, and reducing the IO requirement of your Windows XP (or Vista) guests on the host.

As the Keynotes proceed I’ll try and go over what they are talking about.

Denny

Virtualizing SQL Server? When to and when not to.

Virtualizing servers is huge right now.  And thanks to VMWare it is very easy to build virtual machines.  In most of IT virtualizing servers is a good think.  In the database world, that isn’t always the case.  As we know SQL Server uses a lot of memory and CPU resources.  If you try to virtualize a high load SQL Server you could end up with all the resources of the virtual server being used by the single virtual server.

 Now don’t get me wrong.  If you have a small server with low load which has a SQL Server on it, such as a Blackberry Enterprise Server, that may be an excellent server to virtualize.  Your production CRM database, probably wouldn’t be a good server to virtualize as it probably needs more CPU and memory resources than your Virtual server would be able to afford to give it.  Now that said; if your VM Servers are huge servers with hundreds of Gigs of RAM and lots of CPUs (such as the new HP DL 580 and 585 models) and rack space is tight, then virtualizing SQL Servers might be a good plan provided you can deal with any disk IO issues.

In addition to the CPU and memory concerns there are the disk performance issues to look into.  Typically when setting up a virtual machine, the disk drives are also virtualized.  This means that to the virtual server host the virtual machines disks are simply files stored on the file system.  This probably isn’t the best way to store SQL Server databases (or any system which uses the disk subsystem a lot).  If you can setup your disks to be mapped directly to physically SCSI arrays you can remove this potential problem.  Check your VM solution to see if this is supportd (VMWare does, I don’t know about Microsoft Virtual Server).  If you can provide information about this feel free to post as such in the comments.

 Denny