These days, you can't get away from virtualization. Just about every component in the data center can be virtualized. But while heading up my own deployment at Westminster College, I learned that getting the most out of this technology requires looking at how each piece of the virtualization puzzle, including hardware and software needs, fits together strategically.
Examining each component can help you accurately budget for your virtualization project up front, avoiding costly revisions later. Here is how I broke down, and budgeted for, the individual elements of my server virtualization strategy:
Servers: Virtualization doesn't completely eliminate the use of servers in the data center, but the technology makes huge strides when it comes to reducing the amount of hardware required to operate an IT infrastructure. A server virtualization project does, however, affect the configuration of the purchased servers.
Virtual hosts, such as ESX or Hyper-V servers, run multiple simultaneous workloads rather than the traditional single workload of a typical
As part of our virtualization strategy, we migrated away from a traditional server to a Dell blade server environment. Each of the virtual hosts is a dual quad-core Xeon server with mirrored boot disks and 32 GB RAM. If I were to do it all over again, I'd budget for servers with a minimum of 48 GB or 64 GB RAM in each virtual host.
As for storage, a virtual host server typically won't require much. In most cases, the virtual host is simply a receptacle for the virtualization software; the main storage is on a connected storage area network (SAN). It's very common to see a simple two-disk RAID 1 (mirrored) configuration with just enough local disk space to boot the system. In some cases, a virtual host won't have any storage at all and the system will simply boot from the SAN.
Bottom line: More often than not, RAM becomes the limiting factor on a virtual host, so don't skimp on memory; add as much as possible at the time of server purchase.
Storage: Before server virtualization, individual applications had their own storage capacity and performance (i.e., IOPS) requirements. With virtualization, however, the servers that house these applications are abstracted away from the hardware via the virtualization layer. As such, there are some additional IOPS needs that may not be apparent at first glance.
For example, assume that you've used the Exchange 2010 Mailbox Server Role Requirements Calculator and determined that you need 2,000 IOPS of storage performance. If you're virtualizing the Exchange server, you'll still need that 2,000 IOPS, but you will also need to perform some baseline testing to determine what kind of IOPS overhead is incurred by the operating system itself.
For our small IT environment, we opted for an EMC AX4 iSCSI SAN with 12 SATA and 12 SAS disks. We've since expanded the array to include another tray of 12 15K RPM SAS disks, not because we ran out of disk capacity, but because disk performance was suffering. Disk performance has proved to be the biggest challenge we have in our environment, so we keep a budget line available to address it if necessary.
Bottom line: Make sure to take into account storage capacity needs, as well as performance (IOPS) requirements. Both are equally important to the success of your project.
Hypervisor: There are quite a few hypervisor choices out there, including VMware ESX, Microsoft Hyper-V, Parallel's Virtuozzo and Citrix's XenServer. Regardless of which product you select, make sure you understand how the base product is licensed and what's included in the full feature set.
For example, it's important to understand that VMware Inc.'s vSphere is licensed on a per-processor socket basis. If you opt for a base edition of the product, a socket license includes support for up to six cores per socket. However, the Enterprise Plus edition allows for up to 12 cores per socket. Likewise, some important new capabilities are missing from lower-end editions of the product sets. Before you finalize your hypervisor software budget, be sure to have a complete understanding of exactly which features you are and are not getting with each edition.
I also recommend purchasing a software and support agreement for your virtualization project. Virtualization truly is a major consolidation and moves you close to an "all eggs in one basket" infrastructure, so being able to stay current with the underlying software is important.
Bottom line: Per-socket licensing is becoming more common, but every vendor defines a different core count -- sometimes differing even among products from the same vendor. Make sure you fully understand core counts and product feature sets before making your final decision. Also, consider including some ongoing software maintenance in your budget, which can save you some money in the long run.
Operating system licensing: Regardless of which hypervisor solution you choose, each underlying virtual machine instance still needs to be licensed as if it was a standalone server. This means that you still need server licenses, client access licenses and, optionally, software assurance.
Disk performance has proven to be the biggest challenge we have in our environment, so we keep a budget line available to address it if necessary.
Microsoft, however, has made it easier for organizations to undertake large-scale virtualization
projects through a licensing giveaway in
Bottom line: Look for major licensing shortcuts like Windows Server Datacenter's unlimited virtualization rights and keep virtualization projects from breaking the budget.
Hypervisor monitoring software: Virtual host optimization is a great way to stretch your virtualization investment as far as possible. Makes sure that you eke out every IOPS, and use up every KB of RAM, by assigning the exact amount of computing resources to your virtual machines.
There are a number of companies that provide products to help you with this effort. By buying this software up front, you can avoid additional costs down the line.
Bottom line: Don't skip the monitoring software. Although it's an up-front budget add, it's well worth the small cost in the project lifecycle
It's important not to underbudget when planning your virtualization strategy. Doing so may lead to cutting too many corners early on, which can lead to spending more (time, money, resources) throughout the life of the project just to catch up.
This was first published in May 2010