Evaluate Weigh the pros and cons of technologies, products and projects you are considering.

Choosing the best virtual server storage: A tutorial

Choosing primary storage for virtual servers involves balancing performance, capacity, features, and costs. Learn the key factors to pick the best virtual-server storage system.

By Todd Erickson, News Writer

Implementing a virtual server environment can help small- and medium-sized businesses (SMBs) consolidate IT resources and create a more flexible infrastructure. Choosing the right primary storage for your virtual server environment involves balancing performance, capacity, ease of use and cost.

Whether you plan to use VMware Inc.'s vSphere, Microsoft Corp's Hyper-V or Citrix Systems Inc.'s XenServer virtualization platforms, you'll need a storage system with sufficient performance capabilities and capacity to support the flexible environment virtual servers allow, but at the same time be manageable by a small IT staff and fit in an SMB budget. In this tutorial on virtual server storage, you will learn how to choose the best virtual server storage for your organization, the pros and cons of Fibre Channel vs. iSCSI, and about the other choices you have available.


>>  Getting started with virtual server storage
>>  Storage architecture
>>  Fibre Channel vs. iSCSI
>>  Network-attached storage
>>  Shared serial-attached SCSI
>>  VMware vStorage
>>  From the physical to the virtual



"When planning out the storage side of any virtual environment, determine what kinds of systems you are going to virtualize because a lot of people don't take into consideration the performance and capacity requirements of those systems before building their VM [virtual machine] environments," said W. Matthew Ushijima, a senior consultant for GlassHouse Technologies Inc. "It is important to consider your performance needs from both hardware and software perspective."

Jeff Boles, a senior analyst and director of validation services for the Taneja Group, said that admins should conduct a thorough assessment of current I/O patterns, and then use analysis tools such as Virtual Instruments NetWisdom to determine physical environment storage and performance needs before moving to a virtual environment. Ushijima has also seen Solarwinds Inc.'s Storage Profiler and Aptare Inc.'s StorageConsole Virtualization Manager used to analyze capacity and performance needs.

"Don't virtualize and think you are going to make do with less storage in the process," Boles said. "When you get into more complex applications and more detailed planning, it's best to consult with your application vendors," Boles said.

Editor's Tip: For more information about managing storage in a virtual environment, check out sister site SearchStorage's podcast on storage management tools for virtual environments.


For most environments, networked storage and a multipath architecture will be base requirements. Boles said networked storage will allow you to take full advantage of the flexibility benefits of virtual environments. "You want something that doesn't get in the way of that flexibility," Boles said. "You can move [virtual servers] back and forth between different pieces of hardware, re-provision them, copy them, all that kind of stuff, a lot more easily than in the physical world. You really need shared storage behind the virtual server infrastructure to take advantage of all its capabilities."

A multipath architecture -- having numerous redundant links between servers and storage so the data flow can be broken up into multiple streams and sent over separate links -- is necessary to keep your storage system available in case of a path failure. "In any shared storage environment, I consider [a multipath architecture] to be mission critical," Ushijima said. "I don't care if you are running four servers or 4,000. The last thing you want to do is have a server go down because it dropped its storage connection. The issue only multiplies exponentially for each server you add into a virtual environment."

Editor's Tip: For more information about networked storage, download our free guide about  networked storage for small businesses.


Fibre Channel (FC) is a high-speed technology (up to 8 Gbps) that can be deployed over large distances, but requires relatively expensive equipment and specific administrator knowledge. iSCSI operates over ubiquitous Ethernet technology, but is subject to Ethernet's speed limitations. While 1 Gigabit Ethernet (GigE) is currently the most commonly deployed network technology, 10 Gigabit Ethernet (10 GigE) is available and offers a multiple-factor performance increase. However, a 10 GigE system is more expensive to install and may not be cost-effective for SMBs.

Both Boles and Ushijima recommend assessing your performance needs and available resources to determine which transport system to employ. For SMBs, Boles says iSCSI is the overwhelming leader because of its use of Ethernet and the fact that administrators don't need to have specific FC training to deploy and manage it. "Hands down, if you're looking at a new storage system, and you're an SMB customer, you should be considering iSCSI today," Boles said.

Dell Inc. is no stranger to the SMB market and is a leader in iSCSI storage systems, according to Boles. The company offers iSCSI storage area network (SAN) systems from the EqualLogic PS4000E for SMBs and branch offices to the PS6010XVS, which offers 10 GigE connectors and super-fast solid-state drives (SSDs).

Editor's Tip: For more information on iSCSI SANs, read this guide on  iSCSI SAN best practices.


If you have a predominantly network-attached storage (NAS) environment, it's likely an entry-level file-based system will have more built-in horsepower than an entry-level block-based storage system, Boles said. So you might be able to consolidate more workloads with a NAS system. However, because NAS systems are more widely shared, it might be harder to get a detailed view into which systems are using network resources and what your performance needs are, Boles explained.

Multiprotocol systems that serve both file- and block-based data can be a good fit for SMBs and are now widely available. For example, NetApp Inc.'s Data Ontap operating system supports network file system (NFS) and Common Internet File System (CIFS) NAS protocols, as well as block-based iSCSI and FC. EMC Corp.'s Celerra Unified Storage Platform supports NFS, CIFS, iSCSI, and FC.

Editor's Tip: For more information on NAS, take our quiz on NAS basics.


A newer technology that is moving into the conversation is shared  serial-attached SCSI (SAS), an interface for connecting individual SAS storage disk drives to multiple servers. Shared SAS systems offer simplified management and lower costs, but are limited in distance and you must have SAS-supported servers or SAS adapters.

Dell is also a player in the shared SAS market. The PowerVault MD3200 SAS storage array has single or dual controllers and can scale up to 96 disk drives.

Editor's Tip: For more on this topic, listen to our podcast on  shared SAS.


If you plan on using VMware vSphere hypervisor, consider storage arrays that have integrated VMware's vStorage technology and application programming interfaces (APIs) into their functionality.

VMware's vStorage Virtual Machine File System (VMFS) is a cluster file system that allows simultaneous read and write file access so multiple VMs can access and store data in the same file. Without VMFS, only one server would be able to access a file at a time, increasing system latency and impairing productivity. Storage VMotion is another vStorage technology that allows you to migrate live virtual machine disk files (VMDK) between physical hosts for efficient storage I/O and capacity management.

VMware developed the vStorage APIs to improve the platform's integration with the feature-rich storage arrays and data protection products already on the market. "[The APIs] make use of some array side capabilities and optimize the communication and handling of data between the hypervisor and the array," said Boles.

The vStorage API for Array Integration (VAAI) brings advanced array side features into the hypervisor, including Changed Block Tracking, which allows the storage array to identify changed blocks within VMDK files so it can eliminate previously saved data before transmitting VMDK snapshots over the wire. Another example is VAAI Block Zero, which allows the provisioning of zero-data blocks for populating volumes on the array instead of having the hypervisor provision the zero-data blocks and sending them over the wire. VMware also developed APIs for data protection, multipathing and storage replication adapters.

Editor's Tip: For more on this topic, listen to our podcast on VMware's  vStorage APIs for Data Protection.


When you are ready to select a storage system for your virtual environment, there are tools available to help you prepare a physical-to-virtual (P2V) migration strategy. "There are a lot of products from a variety of vendors that provide tools to scan your existing infrastructure and provide the ability to do virtual assessments," Ushijima said. Neither VMware nor Microsoft offers free P2V planners, although VMware offers P2V Accelerator Services as part of its professional services products.

5nine Software offers a P2V planner for both VMware vSphere and Microsoft Hyper-V platforms. The planner collects data about existing hardware in your data center, its utilization, and application workloads to prepare physical-to-virtual migration plans that take into consideration hardware and business requirements, storage performance and capacity needs, costs, and return-on-investment. 5nine Software offers a free edition with limited reporting and workload and cost optimization capabilities.

"Look for solutions from a networked storage vendor that can give you functionality at the VM level," said Boles. "A lot of the time when it comes to networked storage, you end up just parking a whole bunch of VMs on a LUN or out on a storage system and you have to figure out how to manage your storage without breaking the VMs, and whether you should do things inside the VMs or inside the storage. It's often very hard to connect those two. So look for solutions from your storage vendor that let you do advanced storage operations with your VMs."

Advanced operations include taking individual VM snapshots and recovering from those snapshots without impacting other VMs. Also look for replication capabilities so you have disaster recovery options now or down the road. "You'll get the most bang for your buck that way and extend your storage capabilities," Boles said.

Editor's Tip: For more on this topic and virtual server storage, read our tip on  VMware storage options.

Dig Deeper on Storage for virtual environments