Storage Virtualization Architectures
Symmetric Storage Virtualization
Also known as “in-band” Virtualization
� Data and control info
use same path
� All I/O routed through a
� Manager location varies
� Performance challenges
In the symmetric approach, all I/Os and metadata are routed via a central
virtualization storage manager. Data and control messages use the same
path, which is architecturally simpler but has the potential to create a
The virtualization engine does not have to live in a completely separate
device. It may be embedded in the network, as a specialized switch, or it may
run on a server. To provide alternate data paths and redundancy, there are
usually two or more virtual storage management devices; this leads to issues
of consistency between the metadata databases used to do the virtualization.
The fact that all data I/Os are forced through the virtualization appliance
restricts the SAN topologies that can be used and can cause bottlenecking.
The bottleneck problem is often addressed by using caching and other
techniques to maximize the performance of the engine; however, this again
increases complexity and leads to consistency problems between engines.