The most immediate benefit for administrators is simplified storage management. Virtualization storage software lets administrators manage disk arrays of different types from different manufacturers and scattered in different locations as if they were a single pool of hard disks. This makes daily tasks, like allocating the correct amount of storage to any particular application, a straightforward operation rather than a complex calculation.
Virtualization also streamlines as well as simplifies storage management. Because applications are no longer mapped to specific physical storage devices, disk space doesn’t need to be held in reserve for them. This load balancing improves application performance and allows disk space to be used more efficiently.
A less-visible but equally significant advantage: storage virtualization eliminates application downtime. Many tasks that once required applications to be brought down — swapping out servers whose leases have expired, archiving data, performing backups — can now be executed without any impact on the application.
More Space for More Storage Functions
Storage managers may find that virtualization increases their choices of disk hardware. Managing a heterogeneous storage environment becomes much simpler in a virtualized environment, where applications no longer interface directly with storage devices. “It wouldn’t matter what the hardware is; the application wouldn’t worry about that,” says Capizzi. Managers are freer to mix and match hardware from different vendors, and to substitute lower-cost for higher-cost disk hardware.
However, it’s not yet clear whether virtualization will result in more or less demand for storage. Since storage can be used far more efficiently, Capizzi makes the case that managers will be buying “less hardware, fewer storage arrays, fewer servers.” On the other hand, he notes, virtualization “might make it possible to do things that you couldn’t do before” — which would require more storage capacity.
Many SMBs, Capizzi says, were never entirely comfortable with the level of backup they were performing or with their preparedness for disasters. Virtualization now makes it economically feasible for them to seamlessly replicate data to a second site on a daily basis. But new functions like disaster recovery could require more storage capacity than is saved by virtualization’s increased efficiency.
NAS’ New Appeal
Storage-area network (SAN) and network-attached storage (NAS) technologies will both continue to be used as virtualization becomes more prevalent. Capizzi says that virtualization “doesn’t make anything obsolete that’s there today.”
For the most part, the choice between SAN and NAS is driven by whether an application requests data in files or in blocks. Office applications such as word processing typically store data in discrete files, making NAS structures preferable, while DBMSs typically access data in i/o blocks, giving the edge to SAN storage.
Because of the way its disk drives are accessed, SAN is often selected for complex applications that require intensive disk use and high performance, such as replicating data from numerous servers, and for applications requiring a particularly high level of reliability. NAS gets the nod for simpler applications — and it comes with a less-expensive price tag.
To the extent that there is a choice of storage technology, virtualization may provide a boost to NAS.
The reason, according to Farid Neema, president of research firm Peripheral Concepts in Santa Barbara, Calif., is that virtualization addresses NAS’s greatest weakness — its scalability. Placing more than five or 10 NAS on a network can cause serious management and performance problems. “They each had separate operating systems and separate file systems — it was a nightmare to manage,” Neema says. “But virtualization has completely solved that problem. Now, you see only one file system, managed as one pool of storage.”
As a result, while SAN was once the predominant storage technology, virtualization has put NAS almost on a par with it. The emergence of NAS as a solution equal in status to SAN is demonstrated, Neema says, by the recent spate of “consolidated” or “unified” storage solutions that allow storage administrators to manage both SAN and NAS from a single vantage point.
Another indicator of NAS’ new appeal is found in Peripheral Concepts’ recent survey of end users, which finds that the percentage of data stored on NAS is growing along with NAS virtualization. The number of sites storing more than 30 percent of their data on NAS has increased from 25 percent in 2004 to 44 percent in 2006.
The bottom line: If you are implementing storage virtualization, NAS’ increased manageability may increase functionality and cut costs.