Asymmetric Storage Virtualization
Often implemented as “out-of-band” Virtualization
AGENT AGENT AGENT
Request Data and control info use
Data I/O direct through SAN
Metadata through LAN and/or SAN
Servers need “agent” installed
to intercept access to pass
storage requests via
In the asymmetric approach, the I/O is split into two parts:
First, the server queries the metadata manager to determine the
physical location of the data.
Then, the server stores or retrieves the data directly across the SAN.
The metadata can be transferred in-band, over the SAN, or out-of-band, over
an Ethernet link; the latter is more common as it avoids IP metadata traffic
slowing the data traffic throughput on the SAN, and because it does not
require Fibre Channel HBAs that support IP.
Each server which uses the virtualized part of the SAN must have a special
interface installed to communicate with the metadata manager in order to
translate the logical data access to physical access. This special interface may
be software or hardware. Initial implementations will certainly be software, but
later implementations might use specialized HBAs, or possibly an additional
adapter which works with standard HBAs.