Chapter 2. SAN Volume Controller overview
The SAN Volume Controller combines hardware and software into a
comprehensive, modular appliance that uses symmetric virtualization.
Symmetric virtualization is achieved by creating a pool of managed disks (MDisks)
from the attached storage subsystems. Those storage systems are then mapped to a
set of virtual disks (VDisks) for use by attached host systems. System
administrators can view and access a common pool of storage on the SAN. This
lets the administrators use storage resources more efficiently and provides a
common base for advanced functions.
A SAN is a high-speed fibre-channel network that connects host systems and
storage devices. It allows a host system to be connected to a storage device across
the network. The connections are made through units such as routers, gateways,
hubs, and switches. The area of the network that contains these units is known as
the fabric of the network.
The SAN Volume Controller is analogous to a logical volume manager on a SAN.
The SAN Volume Controller performs the following functions for the SAN storage
that it controls:
v Creates a single pool of storage
v Provides logical unit virtualization
v Manages logical volumes
v Provides the following advanced functions for the SAN:
– Large scalable cache
– Copy Services
- FlashCopy
®
(point-in-time copy)
- Metro Mirror (synchronous copy)
- Global Mirror (asynchronous copy)
- Data migration
–
Space management
- Mapping that is based on desired performance characteristics
- Metering of service quality
Each
SAN Volume Controller node is a rack-mounted unit that you can install in a
standard Electrical Industries Alliance (EIA) 19-inch rack. The nodes are always
installed in pairs, with one-to-four pairs of nodes constituting a cluster. Each pair
of nodes is known as an I/O group.
All I/O operations that are managed by the nodes in an I/O group are cached on
both nodes. Each virtual volume is defined to an I/O group. I/O groups take the
storage that is presented to the SAN by the storage subsystems as MDisks and
translates the storage into logical disks, known as VDisks, that are used by
applications on the hosts. Each node must reside in only one I/O group and
provide access to the VDisks in that I/O group.
There are four models of SAN Volume Controller nodes:
v SAN Volume Controller 2145-8G4
© Copyright IBM Corp. 2003, 2007 3
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