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Using NAS NFS with VMware ESX: Technology pros and cons

Network-attached storage (NAS) is incredibly simple networked storage. It's ease of use for implementations, operations and management is well documented and analogous to VMware Inc.'s VMware

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ESX. This makes NAS an excellent candidate for use as ESX's networked storage.

Using NAS with ESX requires the network file system (NFS) protocol (CIFS isn't supported at this time). A commonly asked user question is "Why isn't NAS NFS used more frequently in VMware ESX environments?" Conventional wisdom says Fibre Channel (FC) or iSCSI SAN storage is a much better fit for VMware ESX, but that might be incorrect.

Pros of using NAS NFS with VMware ESX

It's important to recognize that all ESX guests are stored as *.vmdk files. NAS is architecturally optimized to store, manage and deliver files, and managing files is documented as being much easier to manage than logical unit numbers (LUNs). Therefore, it should logically follow that NAS is, by definition, a simpler network storage than storage-attached networks (SANs).

If there are a few dozen virtual machines (VMs), then a virtual machine file system (VMFS) writing to SAN storage is technically quite good for consolidating VMDKs into a single LUN. But when there are thousands of virtual machines, NAS NFS is a much more efficient network storage methodology.

For example, NAS permits similar VMDK files to be grouped into folders. One folder can hold all of the desktop images, another can hold all of the Microsoft Exchange servers, while a third can hold the SQL servers and so on. In addition, many NAS products bring some very useful and interesting file management capabilities to the table. Among these are data deduplication, information lifecycle management (ILM), quality of service (QoS), zero-impact snapshots, cloning, security and authentication, and mature local and remote copying (asynchronous and synchronous).

Advanced NAS functionality such as deduplication, ILM and QoS can have an enormous positive impact on the storage type and consumption utilized by the VMDKs. VMware users generate a lot of server images, and each one consumes approximately 1 GB to 10 GB of storage. Taken individually, that's not a lot of storage. But in aggregate, it can be considerable.

NAS-based data deduplication (file, block, variable-block and application-aware) can reduce those images by as much as 97% or more, which translates into real, hard dollar cost savings. However, it's important to only utilize this technology when VM application performance service levels aren't too demanding. This makes it excellent for ISO files, templates, desktop images and so on. Deduped VMDKs on an NFS datastore run at a reasonable pace, albeit slower than NAS in general or if using a SAN-based (FC or iSCSI) source. Deduped performance is typically reasonable for low-utilization virtual machines.

The inherent ability of NAS to move application files nondisruptively to different service levels and storage tiers makes efficient use of lower cost storage and archives. But not all production and nonproduction virtual machines require the same performance levels. Some NAS systems can, by policy, determine each VM's performance service-level prioritization, detect what it's actually getting and then ensure that the service level is transparently achieved.

For disaster recovery, many NAS systems work with VMware vCenter Site Recovery Manager (SRM). They also greatly simplify replication by allowing the data for entire groups of virtual machines to be replicated as a single unit.

Cons of using NAS NFS with VMware ESX

The No. 1 drawback associated with using NAS NFS with VMware ESX is supposed to be performance. To some extent, NAS performance does tend to be a bit slower than FC or iSCSI SAN storage. Most VMs will find it difficult to see a difference because storage is rarely the bottleneck. And there are some very fast NAS systems on the market today that make that difference even less noticeable (BlueArc Corp., EMC Corp., NetApp, OnStor Inc. and Reldata Inc.).

Another way to further minimize performance differences is by multiple network connections. These types of connections balance the load and set up multiple paths to different NFS shares.

Another drawback is the perception that NAS NFS doesn't work with the advanced features of VMware ESX. This is no longer true, but there is one exception. NAS NFS works with VMware VMotion, DRS, vCenter SRM, HA-DR and even VMware Consolidated Backup. It doesn't yet work with Storage VMotion (the ability to migrate data between systems nondisruptively to VMs).

One last technology con is the allegation that Windows VM guests can't effectively use NAS NFS because they can't boot from NFS. (Microsoft doesn't support windows boot from NFS at this time.) Some IT pros are surprised that NFS can be used for Windows virtual machines because VMware bypasses this limitation by having built NFS into ESX's disk virtualization layer. ESX handles the NFS protocol, masking the entire operation and protocol from the operating system.

Closing thoughts about NAS NFS with VMware ESX virtual machines

NAS NFS is an excellent networked storage option for VMware ESX virtual machines because it's simple to use and offers outstanding value.

In addition, a VMware environment can have mixed networked storage of NAS and SAN, and apply them where they fit best. This makes the most sense, especially when one or the other already exists in the infrastructure.

About the author: Marc Staimer is founder and CDS at the 11-year-old marketing analyst and consulting firm Dragon Slayer Consulting. He is a regular contributor to TechTarget venues.


This was first published in March 2009

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