Switches have emerged as a crucial element
in any storage area network
(
SAN) infrastructure, interconnecting and
managing traffic between the various storage systems and server
elements on the SAN -- sometimes supporting hundreds of ports on
a single switch. But switches have evolved to be far more than
just network "traffic cops." Today, many SAN switches provide
powerful features that can help administrators organise and
manage the storage network, including
storage virtualisation,
provisioning/
zoning, interswitch link (ISL) trunking,
performance planning and security features like authentication.
This overview highlights the
characteristics of high-end switches.
Blade switches
Blade switches are basically modular switches designed to fit in
blade chassis produced by major manufacturers like Dell Inc., IBM,
and Hewlett-Packard Co. (HP). Although there are no features or
capabilities unique to blade switches, the blade form factor offers
a substantial advantage to blade server users. By mounting a blade
switch, other blade servers in the chassis can be connected through
the blade switch to the rest of the network. This is cleaner and
more convenient than cabling each blade server to an external
switch. However, it's important to remember that blade switches
generally offer limited scalability, and they are more expensive to
deploy because blade chassis are not yet mainstream. Blade servers
may also experience issues booting from the network through a blade
switch.
McData Corp.'s 4314 and 4416 Fibre Channel (FC) switch models
support the Dell PowerEdge 1855, both sporting a total of 16 FC
ports running up to 4 Gbps. Similarly, a McData FC blade switch
module with 10 or 20, 4 Gbps FC ports can be purchased for the IBM
eServer BladeCenter. As another example, the HP p-Class BladeSystem
is served by a 10 port, 4 Gbps McData SAN blade switch.
Director switches
Enterprise data centers often incorporate large director-class
switches that offer massive scalability for the SAN, yet can be
managed as a single platform. In addition, director switches
feature fault tolerance, nondisruptive software upgrades,
hot-swappable components, redundant power
and cooling systems, and advanced security features. Director
switches can frequently support multiple network protocols and
can even be logically organised into multiple virtual switches.
Heterogeneous server and storage system
support is critical for a director switch. The two principle
issues with director switches are cost and management: Directors
are significantly more expensive to acquire than other switch
classes, and the general lack of friendly wizard-driven
interfaces usually means that management tasks can be more
cumbersome and time consuming.
You'll typically find products from Cisco Systems Inc., Brocade
Communications Systems Inc., and McData at the high end of the
switch spectrum. For example, Cisco's MDS 9513 is one of the
largest director switches available, sporting as many as 528 FC
ports in a single chassis, each port capable of 1, 2, 4 or 10 Gbps.
The 9513 includes support for
VSANs and VSAN routing, along with advanced
security features. Brocade's SilkWorm 48000 SAN director scales
nondisruptively from 32 to 256 active 4 Gbps FC ports in a
single domain, supporting enterprise management, high-volume
transaction processing and backup tasks. Finally, the McData
Intrepid i10K director provides up to 256 FC ports running at 2,
4 or 10 Gbps, depending on the service modules that are
installed. All these directors are noted for their reliability
and administrative features.
Intelligent switches
In terms of SAN switches, "intelligence" suggests the presence
of advanced features, like storage virtualisation, remote
mirroring, data sharing, protocol conversion, quality of service
(QoS) management and strong authentication/security features. As
storage networks become more sophisticated and support a growing
range of storage products, adding intelligence to the switch offers
compelling benefits -- most notable is the centralisation of
network-based services. Rather than managing network services
handled by a variety of applications running through individual
servers in different locations around the network, managing an
intelligent switch potentially lowers labor
costs and software licensing costs (e.g., volume managers) and
improves resource utilisation by reducing overprovisioning.
However, intelligence has nothing to do with the size of a
switch. Thus, director-class and intelligent switches are not the
same thing. A director switch may not have many intelligent
features, if any, and often must be configured with service modules
to support intelligent functions. Conversely, intelligent features
are appearing more frequently in blade switches and even in some
lower end products, like edge/workgroup switches. ***