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The host only knows about the logical disc, so any changes to the metadata mapping goes
on without the host knowing. This means that data can be moved or replicated to a different
physical location without any effect to the client. If data has been moved or replicated,
the metadata is updated to represent the data’s new location, thereby freeing up space at its
former location.

NOTE Metadata is sort of a map of where your data is stored on the SAN.
By migrating data, the IT manager can perform a number of day-to-day tasks much easier:

• Moving data off an over-utilized device
• Moving data to a faster storage device
• Migrating data off of older storage devices (for instance, those being replaced or
returned when a lease period has ended)

Pooling
IT managers are able to better utilize their storage equipment through virtualization. This is
accomplished through pooling.
For instance, when storage capacity is pooled, IT managers don’t have to try and find
open space on certain drives to allocate space for a host or server. When the system is
pooled, a new logical disk can be allocated from the pool. It also allows an existing disk to
be expanded.
This is an extremely efficient system. Through pooling, all the available capacity in your
disks can be used. In a conventional environment, a whole drive would have to be mapped
to the host. If the drive has more capacity than is needed, this space is wasted. If the drive is
too small for this use, you run the risk of running out of space and having to add additional
drives.
Storage can also be assigned when it is needed, so you don’t have to guess how much
space is needed. Also, if you need more capacity overall, simply adding extra drives can
help your entire organization’s storage needs. For instance, as Figure 12-3 shows, let’s
say your marketing, production, and administrative departments all need more capacity
in their individual servers. If you are pooling your drives, you just need to add one
drive. In a traditional environment, you’d have to buy (and install) three separate
drives.
Ease of Management
Storage virtualization makes management of your data much easier. Even though data is
scattered throughout many devices, it all appears to be in one place, on one storage device.
This allows you to manage your data centrally.

Risks
Like a moon shot or dating an old girlfriend’s best friend, there are risks involved in storage
virtualization. Before moving all your data onto a new SAN, it’s a good idea to understand
what’s involved with the transition.