Storage Area Networks For Dummies®

Chapter 15: Everything You Ever Wanted to Know about Virtualization
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Using virtualization for better performance
Mapping extent pools from physical devices rather than through direct mapping
has benefits. Virtual disks that map through extent pools can be spread
across many more physical devices than direct mapping. By spreading the
I/O workload across many spindles in the pool, you can get better performance
from a virtual disk than through a directly mapped LUN.
In Figure 15-13, you can see where multiple physical spindles can be virtualized
through the abstraction layer and pooled into a LUN that spans not only
a lot of physical spindles but also multiple storage arrays, controllers, and
fibre-channel ports. Also, because the virtual LUN is now made up from the
extent pool using a virtual volume that utilizes multiple controllers, RAID
groups, and even storage arrays, the virtual LUN can be much more fault tolerant
than a physical LUN.
Virtual pools of storage can also be divided up by capabilities or cost. Once
divided, data can be moved between the pools at any time, even while the
applications are running on the servers. The ability to move data at will
provides a way to move data between higher-cost production storage and
lower-cost backup or archive storage. Moving data between these tiers of
storage as the data ages and becomes less relevant to the company is called
Information Lifecycle Management (ILM). (See Figure 15-14.)
21+3
RAID 5
Virtual LUN
Virtual Abstraction Layer
Virtual
Volume
7+1
RAID 5
7+1
RAID 5
7+1
RAID 5
Physical LUNs
Physical Arrays
Figure 15-13:
Enhancing
disk performance
through virtualization.
Storage Array Storage Array Storage Array
Extent Pool
(Virtual Storage Pool)