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Best storage for virtual servers: Pros and cons of FC, iSCSI and NAS

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Virtual servers need a good shared data storage system. All major networked storage protocols work with virtual machines, but some are better than others in certain environments.

Choosing a data storage system to use with virtualized servers is one of the most critical architecture choices you’ll have to make, and one of the most challenging. There are many options available, but there’s no single type of networked storage that’s hands down the best for virtual servers. Each environment is different and what works well for one may not work well for another.

Fibre Channel (FC) has been the traditional choice for virtualization, but iSCSI and network-attached storage (NAS) have become increasingly popular alternatives that can provide good performance for more limited budgets. Let’s look at the characteristics of each networked storage type and review its pros and cons.

Fibre Channel storage

For performance and reliability it’s hard to beat FC storage, but the performance comes at a price in terms of both dollars and complexity. Because of its deep roots in the data center, FC is generally the most popular storage choice for larger virtual environments, based mainly on its speed (currently 8 Gbps with 16 Gbps becoming available) and reliability. FC storage networks tend to be isolated and thus more secure than Ethernet-based storage devices. But Fibre Channel requires special host bus adapters (HBAs) and switches that are

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more expensive than comparable Ethernet components.

Emerging techs: FCoE, 10 GbE and CNAs

Newer technologies are now available, such as Fibre Channel over Ethernet (FCoE) and 10 Gbps Ethernet (10 GbE), that offer alternative architecture choices while providing big boosts in performance and throughput. FCoE provides encapsulation of a native Fibre Channel (FC) frame into an Ethernet frame to bring together the benefits of FC architecture over an Ethernet infrastructure. FCoE can eliminate the need for costly Fibre Channel hardware. 10 GbE provides a huge speed boost over conventional 1 Gbps Ethernet, but requires network interface cards (NICs) and switches that are specifically designed for 10 Gbps.

FCoE and 10 GbE are directly related to each other as you can only run FCoE on 10 Gbps networks. Converged network adapters (CNAs) combine the two technologies onto a single network adapter, eliminating the need for separate FC and Ethernet adapters. CNAs reduce the number of server adapters, cables and switch ports required, which can help reduce expenses. FCoE, 10 GbE and CNAs are great technologies, but like any new tech they can be expensive to implement for early adopters.

 

So, implementing a Fibre Channel network from scratch can be costly. Also, FC environments are more complex to implement and manage as their configuration is very different from a traditional network infrastructure. While most companies have staff with network administration skills, many don’t have the same resources for FC storage-area network (SAN) administration. Designing and managing a SAN architecture usually requires specialized training that can further add to the expense of implementation.

Advantages of using FC storage

  • Commonly deployed enterprise storage architecture; many environments may have existing SANs
  • Typically the best performing storage due to higher available bandwidth
  • Isolated FC fabrics are more secure; logical unit number (LUN) zoning and masking can be used to control access
  • Able to boot from FC storage (boot from SAN) so local host storage isn’t needed
  • Block-level storage that can be used with VMware vSphere VMFS volumes

Disadvantages of using FC storage

  • Typically the most expensive storage option to implement from scratch
  • Requires specialized and expensive components such as switches, cables and HBAs
  • May be complex to implement and manage; typically requires dedicated storage administrators
  • Fewer security controls available; authentication and encryption are complicated to implement

If you plan on having many high disk I/O virtual machines (VMs) running on your hosts then you should seriously consider using FC storage for maximum performance. Fibre Channel over Ethernet (FCoE) is also an option that allows you to run FC storage over traditional Ethernet components, but it can be just as expensive to implement as it requires 10 Gbps Ethernet (10 GbE) networking and special switching gear.

If you already have an FC SAN in your environment, then using it with virtualization just makes sense. And expanding an existing SAN is much easier and cheaper than implementing a new one. You really can’t go wrong with FC storage if your budget can afford it and you can handle the management complexity.

This was first published in September 2011

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