Most of today's enterprise-class storage networks employ Fibre
Channel technology for its high performance and rich features. But
FC is still expensive to deploy, configure and manage -- well
beyond the means and technical capability of many small to midsized
IT departments. By comparison, IP network (e.g., Ethernet)
technology and components are inexpensive and readily available;
offering ubiquitous deployment from the SOHO to the largest
corporate user LAN. By supporting SCSI storage commands across the
IP network, organisations of all sizes can now deploy inexpensive
storage networks capable of transporting storage data anywhere
Internet access is available. As with FC storage networks, devices
like switches and routers play critical roles in IP storage
performance by segmenting storage traffic, keeping that traffic
separated from regular LAN user traffic, and maintaining security.
The most current IP switches and routers even provide high-end
features such as active/active clustered failover, failback, and
multipathing capabilities for improved reliability.
Consequently, choosing an IP storage switch or router will have
a profound impact on your IP storage implementation: While the
actual product list is relatively small -- dominated by
well-established communication vendors -- the choice of an IP
switch or router demands careful consideration of issues including
port speed, segmentation, interoperability, security, and
application compatibility. Now that you've reviewed the
essential issues involved in any storage network
scaling project, this segment will first focus on specific
considerations for IP storage switches and routers. After that,
you'll also find a series of specifications to help make
on-the-spot product comparisons between vendors, including
Brocade Communications Systems Inc., Cisco Systems Inc., Emulex
Corp., and others.
Determine the need for an IP storage network. The first
purchase consideration should be to evaluate the need for an IP
storage network in the first place. If a site already deploys 100%
FC, it may not make sense to add IP storage to the mix. It's
another storage infrastructure that needs to be implemented and
managed. However, the price/performance tradeoff can be compelling;
by implementing an inexpensive and well-understood IP storage
infrastructure, many more servers can be cost-effectively
interconnected to the fabric, and this in turn can dramatically
improve server resource availability for the entire workgroup or
organisation -- a good first step in server/storage consolidation.
Also consider the applications that will run on the IP SAN. Some
applications are better-suited for an IP SAN, while others may
require an FC SAN. Lab testing can help identify any potential
application compatibility problems.
Consider the logical separation points. While smaller
organisations could deploy IP storage networks only, larger IT
departments with a current FC investment must decide how IP storage
fits in the overall storage picture. For example, it might be
prudent to place user data on IP storage, while mission-critical
applications and data remain on FC. Similarly, IP SANs may be
appealing in remote offices where a smaller staff can easily be
supported, and storage data can be exchanged with the main data
center across the Internet. IP switches and routers should be
selected with such criteria in mind. Industry experts note other
technical purchase considerations including SAN segmentation
support and cross domain inter fabric routing; including mapping
zones across SAN segments. Virtualisation is often used to
segregate IP SANs (Cisco has coined the term VSAN).
Consider IP SAN security features. The ubiquitous nature
of IP can impair IP SAN security. It is important to keep the IP
SAN logically separated from the rest of the user LAN. Otherwise it
is possible that sensitive corporate data may "leak out" across the
LAN and onto the Internet unexpectedly. In addition to good IP SAN
planning, you should also evaluate the authorisation and
authentication capabilities of an IP switch or router to ensure
that no unauthorised users can access the IP SAN. For example,
Brocade's FC4-16IP Blade for 48000 Director includes RADIUS. By
comparison, Cisco's 9216A and 9216i Multilayer Fabric Switches
includes support for IPsec, Internet Key Exchange (IKE), and
virtual SANs (VSANs).
Consider the ports and connectivity features. Since iSCSI
is often implemented to supplement a FC SAN, the switch and router
hardware will implement both IP and FC ports on the same physical
device. Evaluate the available ports and their performance to be
sure that an iSCSI investment will offer adequate expandability.
For example, Brocade's iSCSI gateway combines two Gigabit Ethernet
ports and two 2 Gb/s FC ports into a single device -- this approach
is adept at linking servers with both iSCSI and FC storage systems.
Also pay attention to the device's protocol support, and
translations between protocols should accommodate your specific
needs. For example, an IP switch or router may handle translations
like iSCSI to FCP, FCP to FCIP, FCP to iFCP, FCP to FICON, FCP to
SRP, and so on. Advanced features like active/active clustered
failover, failback, and multipathing capabilities all help to
improve the reliability and availability of the IP SAN.
Consider the available management tools. All IP switches
and routers will provide some type of management software, but it's
important to evaluate the effectiveness and flexibility of the
software before making a purchase decision. Tools should generally
allow for device configuration and maintenance. Management tools
may allow performance monitoring for resource utilisation analysis
and service level management. Intelligent health monitoring
features can identify potential faults and alert a technician.
Enhanced features like ISL trunking aid inter-switch performance
and port consolidation. Today, management tools are increasingly
heterogeneous, supporting multiple vendors' devices through a
single console.
Consider WAN features like compression and acceleration.
IP devices intended to operate over WAN connections may include
features designed to optimise bandwidth. FCIP compression reduces
redundant data, shrinking the shear amount of data passed across
the WAN. Acceleration features like FCIP write acceleration and
FCIP tape acceleration improve storage traffic across distance by
eliminating the latency caused by command acknowledgements. For
example, Cisco's MDS 9000 IP Storage Services Modules claim
compression ratios of 2:1 to 30:1, while supporting both FCIP write
acceleration and FCIP tape acceleration.
The IP storage switch and router specifications page in this
chapter covers the following products:
- Brocade Communications Systems Inc.; FC4-16IP Blade for 48000
Director
- Brocade Communications Systems Inc.; Brocade iSCSI
Gateway
- Cisco Systems Inc.; 9216A and 9216i Multilayer Fabric
Switches
- Cisco Systems Inc.; Linecard - IPS8
- Cisco Systems Inc.; Linecard - MPS-14/2
- Emulex Corp.; Model 725 iSCSI Storage Router
- Emulex Corp.; Model 735 FCIP Storage Router
- Hewlett-Packard Co.; StorageWorks 400 Multi-Protocol
Router
- SANRAD Inc.; V-Switch 3800 Enterprise iSCSI Switch
- Woven Systems Inc.; EFS-1000 10GigE IP fabric switch
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