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Server virtualization client concerns

These 10 server virtualization client concerns are based on questions posed by end users, your potential customers, who could benefit from server virtualization support services. Whether you're trying to pitch a new virtualization service or product suite to a customer, help them evaluate those offerings, or walk them through a deployment, you're sure to find some handy insights in this collection of FAQs posed by members of our sister site

1. Which is the better server virtualization product: Microsoft Virtual Server or VMware?
A comparison of the two could easily fill a whole article. Microsoft Virtual Server 2005 R2 is available as a free download (although you obviously need to have paid for any licenses for the OSes to be run in it), as is VMware Server. One big difference between the two appears to be ease of use: Virtual Server requires a little more work to get up and running and work with, while VMware is more wizard-driven and that much easier to get a handle on. The other difference seems to be performance, but this is debatable. I have read a few newsgroup postings that seem to indicate that Virtual Server is slightly faster with regard to some I/O operations. Most people don't seem to be able to find any real difference between the two that would motivate them to switch from one to the other.

Get more comparative information on virtualization vendors. 2. I have been told that any SQL Server should not be moved to a virtual server. Is that the case? Can I use VMware to move SQL Server to a virtual server?
Should you or shouldn't you virtualize SQL Server? Technically, you will have no problems doing so, but you may run into issues later when it comes to performance. You can always throw more virtual CPU and memory at SQL, but eventually the overhead of writing to virtual disk files may bite you. You can of course set up raw device mappings (RDM), but I will suggest to you what I suggest to most people: If you are configuring a RDM to get the better disk performance, and not to test virtual clusters, you may be better off going with a separate physical server with real disks. There is absolutely no reason not to run development instances of SQL server in a virtual environment, but depending on the demands of your production environment, a virtualized, production SQL server just might not score high enough on performance tests.

Get more information on SQL Server channel issues. 3. Using VMware, I'm told you can make the servers automatically fail over to another physical machine if it detects a server error. Can this work over a different name space (i.e. failing over to a physical box on a different VLAN at a different building)?
The process you are referring to is known as VMware high availability (HA), one of the new features of VMware Infrastructure 3 (VI3). VMware HA enables virtual machines (VMs) running on ESX 3 hosts that belong to VMware HA-enabled clusters to fail automatically over to other ESX 3 hosts that belong to the same VMware HA-enabled cluster. The question then becomes, "Can a VMware HA enabled cluster contain ESX 3 hosts in separate buildings and/or separate VLANs?"

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The VMware cluster prerequisites state that "In general, DRS and HA work best if the virtual machines meet VMotion requirements..." Of the VMotion requirements, there are two that present a problem for separate buildings and separate VLANs. VMotion requires that participating hosts use shared storage -- typically this is a storage area network (SAN) attached to the hosts by means of a fibre connection. VMotion also requires a private gigabit ethernet migration network between all participating hosts.

For the continuation of this response, visit 4. Our architecture team, which doesn't know our Microsoft environment, wants to migrate all Exchange infrastructures to a virtualization environment using VMware. Do you think this is a great error?
Your architecture team is partly correct. There is absolutely no reason why you should not be able to virtualize your Exchange front-end servers (or client access servers as they are called in Exchange 12 terminology). Even under stress, a virtual machine (VM) with a single CPU and 512 MB-1 GB of RAM should be plenty for an Outlook Web Access (OWA) server. But you can tell your architecture team to hold off on any plans to virtualize the Exchange back-end servers (mailbox servers in Exchange 12). While technically this plan of action is not a problem, it falters under heavy performance loads. Exchange creates an extremely high amount of disk IO. Virtual disk files simply cannot keep up with what Exchange can throw at them when Exchange is being hit hard. There is a loop-hole: raw device mappings (RDM). You can configure a VM to talk directly to a LUN on your SAN using RDMs. This does make it possible to virtualize back-end Exchange servers with satisfactory performance.

Get more information on Exchange channel issues. 5. Why are I/O limitations making the news as a possible negative effect of virtualizing servers?
Vendors (and consequently IT staff) tend to focus on processor speeds and memory bandwidth, and leave I/O design as an afterthought. It's certainly true that, when running multiple virtual machines on the same physical server, you'll have a significant amount of contention for disk resources. You can simulate the same thing on your desktop: Measure the amount of time it takes to copy two large files sequentially vs. copying both at the same time. Now, imagine running five to 15 separate operations with varying patterns or activity. So, the bad news is that I/O bottlenecks are likely to occur in virtualized environments.

The good news is that you have several options for increasing I/O capacity on servers. The main statistics you'll want to measure are total disk throughout (e.g., 30 MB/sec), and I/O operations per second (IOPS). The latter is particularly important, as I/O requests from virtual machines can be small and frequent. For local storage, you have several options: SAS (Serially-Attached SCSI), SCSI, SATA and ATA. Generally, SCSI and SATA interfaces will give you the better performance due to their ability to perform concurrent I/O. Placing virtual hard disks on separate physical hard disks can greatly improve performance and reduce overall contention. Additionally, some RAID configurations can help increase overall throughput.

For the continuation of this response, visit 6. How should Virtuozzo be compared with offerings from VMware, Microsoft and XenSource?
I usually refer to products such as SWSoft's Virtuozzo or solutions from Softricity as "application-level virtualization" (as opposed to "server-level virtualization" which is the approach taken by Microsoft Virtual Server, Xen, and VMware). The major advantage of this approach is that it can be extremely scalable -- hundreds of instances of a particular application can run on a single physical machine. In many cases, it can be quick and easy to setup virtualization at the application-level and to provide access to end users. There are, however, drawbacks -- mainly, aspects such as operating system settings, patch levels, security configuration and device drivers are all defined at the system level. If your application requires these types of changes, application-level virtualization may not be the best fit. Also, complex network and configuration requirements for multi-tier enterprise applications may not be easy to configure. Overall, however, this approach can be economical and can be a great way to run multiple instances of a relatively simple application.

Get methods for packaging virtualization services for SMBs. 7. Suppose I have installed a guest operating system on a host OS. For example, on Linux I have configured Windows XP as guest operating system. How do I run the applications on Windows XP? How do I access this guest operating system from other computers on my LAN?
The rule of thumb is that just about everything should work as it does on a physical machine. You can use ISO media, file shares or direct downloads on the virtual machine (VM) to get the installers you need, which leads to your second question: There are several networking options. If you want your VMs to be accessible to the LAN, you can use a bridged networking configuration where the VMs will be connected directly to a physical network connection on the host. As long as the VMs have valid network addresses, other users and computers on the network should be able to access them as if they were virtual machines. Another virtual networking option is to place connect the VMs on an isolated virtual network (which improves manageability and security).

Get an indepth guide to selling and deploying virtualization projects. 9. How is Xen different from other virtualization products? What operating system does Xen support?
To answer your first question, Xen has a lighter-weight implementation and hooks into the guest operating system, but in the future it will be able to support native operating systems. Look for lots of info on Xen as Intel and AMD release their virtualization-friendly chips this year.

To answer your second question, Xen supports paravirtualization, in which the guest operating systems must have kernel extensions placed into their code so that they can cooperate with the Xen hypervisor (the virtualization software). Many mainstream Linux distributions like Red Hat, SuSE and Debian (along with many others as well) have those kernel extensions available and can thereby serve as the base operating environment for Xen (referred to as the host OS) as well as operating as guest OS systems. Xen 3.0, when running on the latest generation of chips from Intel and AMD, both of which have hardware extensions that better support virtualization, can run unmodified operating systems. In particular, this means that Xen 3.0, operating on machines with these chips, can host Windows guest systems.

Get more information on virtualization management and planning. 10. There are so many options for virtualization but I'm not sure it's right for my data center. Is there a free, open source option?
The most popular virtualization product is VMWare from EMC. It is widely regarded as an excellent product, but it expensive. Its cost has kept it out of reach for many organizations. Setting cost aside, most previous virtualization products have imposed performance penalties on the virtual operating systems: An application executing within a virtual OS performs poorly compared with the same application running on a native OS. This performance hit is caused by the intervening levels of software interposed between the application and the underlying native OS.

There is a product that can address both virtualization problems: Xen. Xen is a small (< 50 KLOC) virtualization product available under open source licenses. Due to its small size and clever engineering, Xen imposes far less of a performance penalty on running applications than other virtualization products.

Get more comparative information on virtualization vendors. 8. Can virtual machines benefit from added memory? Specifically, will VMware or Microsoft Virtual Server be able to take advantage of having more than 4 GB RAM on a 32-bit system with Windows 2003 Enterprise Edition?
Virtual machines (VMs) that are running on the 32-bit edition of Microsoft Virtual Server are limited to using up to 3.6 GB of physical memory each. However, your virtual Server host systems can certainly take advantage of more physical memory. The overall limit is based on the amount that is supported by the host operating system. So, for example, if your Windows Server 2003 Enterprise Edition computer has 12 GB of physical memory, you can allocate this among your VMs. In general, having more memory will allow you to run more virtual machines concurrently (with better overall performance). On many modern hardware systems, adding memory can be one of the most cost-effective ways to scale virtualization.

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