IT managers have been advised to be wary of vendor hype surrounding storage
virtualization as it is a technology that is poorly defined, misunderstood and
not widely used, according to Dr. Kevin McIsaac, an advisor at research firm
Intelligent Business Research Services Pty Ltd. (IBRS).

Despite all the hype, McIsaac said over the next two years network based storage
virtualization will remain a niche, while thin provisioning will enjoy rapid
adoption in the enterprise.

And while McIsaac readily admits server virtualization is one of the best IT
infrastructure trends to emerge in many years, he said the situation is very
different when it comes to storage virtualization.

"This idea of being able to layer virtualization over existing storage
arrays is seriously flawed," he warned.

McIsaac said a reasonable definition of storage virtualization is "the
abstraction of logical storage from physical storage". However, given the
sweeping nature of this definition it is not surprising that the technology
creates confusion.

"The first step in understanding storage virtualization is to recognize
that many of today's commonly used techniques and technologies are examples
of virtualization including a file system or a storage array," McIsaac
said.

Rather than thinking of it as a specific new product or feature, McIsaac said
it should be thought of as a broad technique that can be deployed at any layer
of the storage hardware and software stack to simplify the storage environment.

"Network based virtualization, which involves using a device in the network
to provide an abstraction layer over storage arrays, is usually what vendors
mean when they refer to storage virtualization," he explained.

"The idea is to layer virtualization over existing arrays to create a
single storage pool, simplify management and eliminate vendor lock-in. But this
idea has significant flaws."

Organizations typically moved to an external storage array, either via a SAN
(storage area network) or a NAS (network-attached storage), to achieve higher
utilization by sharing the same pool of spare disk across multiple servers.

McIsaac said applying network based storage virtualization to pool arrays isn't
likely to improve this environment if efficient utilization hasn't already been
achieved.

"Network-based storage virtualization results in a lowest common denominator
view of the infrastructure, eliminating the value added features of the array;
this investment in the advanced features of the storage array could be lost
making it a waste of money," he said.

"Also the addition of the virtualization layer adds yet more complexity
to the environment, it can introduce a performance bottleneck and add yet another
potential.source of failure. And while it may eliminate vendor lock-in at the
storage array it replaces it with lock-in at the virtualization layer."

McIsaac believes array-based virtualization is the best solution and the next
major step forward is thin provisioning. This is a provisioning mechanism for
allocating storage capacity on a just-in-time basis from a single shared capacity
pool. In this approach the physical storage is only allocated when it is used,
not when it is provisioned.

"Administrators typically over allocate storage because of the complexity,
impact and additional work to grow capacity. For example, if an application
requires 50G bytes the DBA will request 100G bytes for head room, then the storage
administrator doubles that just to be sure and provisions 200G bytes,"
he said.

"Thin provisioning eliminates unused storage, reduces capital costs and
simplifies capacity planning. While it isn't widely used at present its adoption
will accelerate rapidly as vendor support widens and administrators become aware
of its benefits.

"I'm predicting that over the next 18 months thin provisioning will become
as pervasive as other array-based virtualization features such as RAID and snapshots."

McIsaac advised administrators to review current vendors and technologies recognizing
that "some vendor lock-in is unavoidable".

He said avoid using network based storage virtualization, instead minimizing
the number of array vendors deployed in the SAN or NAS.

ARD Consulting IT manager, Eric Biggsley, said when it comes to storage its
all about simplicity which is why he opted for an iSCSI SAN.

"Also I was making my purchasing decision when VMWare announced it would
be adding iSCSI support," he said.

"This was great news because a SAN is necessary to get the most out of
virtualization, but I didn't want to do it with Fibre Channel because it was
just too costly and we didn't really have the resources to support it."

Since then Biggsley has combined server virtualization with SAN technology.

"Virtualization was one of the key drivers behind the selection of an
iSCSI SAN," he said.

» posted by abennett

Computerworld Australia

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