At the file level, virtualization comes in handy when companies develop too many islands of network-attached storage. "[If] your users are storing data all over the place, and you can't back them all up under a single roof, you use storage virtualization to bring all that under a single umbrella, and everyone accesses it through a common [naming convention]," explains Ashish Nadkarni, principal consultant at GlassHouse Technologies Inc.
At the tape library level, virtualization is used for making online storage appear as tape to the backup software.
2. Do you want host-, network- or array-based virtualization?
When deciding what type of virtualization is best, "it really comes down to what problem you're trying to solve and what kind of vendor affinity you have," Nadkarni says.
For most IT units, having host-based virtualization is a given, since volume managers run on the host. More often than not, you'll see host-based virtualization in a storage-area network (SAN) environment.
"Array-based virtualization is more of a function of which vendor you're going with for your primary storage," Nadkarni says. For example, with some Hitachi Data Systems storage products, virtualization can be deployed by enabling an existing software key within HDS's Universal Storage Platform or its Network Storage Controller. "So you'll go with array-based if you plan to buy a Hitachi frame for your Tier 1 storage," he says.
Network-based virtualization is typically used if you plan to make your SAN a multiprotocol storage network and in doing so are porting the network intelligence -- which also includes virtualization. Cisco Systems Inc. and Brocade Communications Systems Inc. are now coming out with products that let you virtualize within the network, without the need for an array or a host to do anything.
Some products blur the lines between host-, array- and network-based virtualization. "Products like Seanodes' would be considered host-based virtualization because you're virtualizing over the nodes," Hacopians explains. "You could also think of it as network-based, because you're virtualizing and spreading it across and letting the network take care of itself."
Industry watchers agree that virtualization might be easier to implement and cost less if IT groups stick with their vendors. "If you're primarily in a Hitachi environment, for example, array-based virtualization is probably going to make the most sense," Nadkarni says. "If you're a Cisco SAN, and you already have the infrastructure to implement Cisco virtualization, then network-based makes more sense."