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Chapter 4 FCIP over IP/MPLS Core
Conclusion
In addition to those listed in Table 4-2, other requirements include provisioning, error monitoring, and
end-to-end management.
Remote Tape-Backup Applications
In an enterprise network, certain sites (remote branches or small offices) can have a small SAN that
connects a few servers to the storage arrays. Backing up and restoring these servers over the WAN is a
fundamental component of disaster recovery operations. Extending tape backup over a wide area
imposes stringent requirements for efficient tape backup and recovery operations. These requirements
include no data loss, low latency and jitter, monitoring of the link, and high security.
Slow wide area links can increase backup time and can make it impossible to complete backup within
the allocated time period (or “window”). Distance is not a major limitation for backup to tape
applications as long as it is possible to predict delay requirements. For backup to tape to be as efficient
as possible, Cisco recommends sustaining a certain speed so that a continuous stream of data is sent to
tape. Backup performance has been found to be best when the tape can accept a continuous stream.
Backup to tape transfer over the WAN is asymmetrical in nature. The asymmetrical nature of
tape-backup data transfer creates unique challenges when designing SAN extension networks.
Tape “pipelining” technology helps to extend tape drives thousands of kilometers, thus making remote
tape backup an essential component of business continuance and disaster recovery applications. The
efficiency is achieved by implementing buffering and error-recovery mechanisms. The concept is similar
to spoofing; even though the server and tape controller are separated by a large distance, they behave as
if they are co-located. The tape pipelining technique relaxes the design constraints of SAN extension
technologies.
A typical solution includes transport over MPLS, which provides all the necessary QoS requirements
required by tape backup applications. The Cisco solution provides necessary provisioning, management,
bandwidth optimization, and performance parameters that are critical to implement tape backup
applications. The Cisco solution can scale as bandwidth requirements increase and still maintain the QoS
requirements required to support this application.
Conclusion
IP is becoming a protocol of choice to transport storage traffic across WANs and MANs. The IP/MPLS
networks of SPs can be used to transport FCIP and iSCSI efficiently for disaster recovery and business
continuance solutions. SPs can leverage their current infrastructure with out much modification to the
network elements to transport FCIP and iSCSI. By providing storage services, SPs can increase the
utilization of their network while providing value-added services.
Disk mirroring Varies depending on
storage array.
Typically maximum 50
MB per storage array.
< 1–5 ms for
synchronous.
Asynchronous
replication tolerates
higher latency (100
ms).
Synchronous or
asynchronous.
Synchronous
applications are very
sensitive to delay.
Asynchronous are
less sensitive to
delay.
File access OS dependent. Depends on the OS
and application
above it.
Table 4-2 Application Requirements
