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Distance Extension
Best Practices
To implement a successful extended-distance BC/DR solution, follow
a set of best practice conventions as follows:
1. Use dedicated bandwidth and rate limiting - If possible,
negotiate dedicated bandwidth as part of the SLA with the
network service provider. Enable intelligent port rate limiting to
ensure the ingress data rate does not exceed the negotiated
bandwidth.
If dedicated bandwidth is not available, quality of service (QoS)
processing applied to shared bandwidth may be acceptable.
Ensure other applications using the shared bandwidth are
characterized and understood. Best-effort shared bandwidth is
not recommended.
2. Optimize IP WAN use - In addition to rate limiting, employ
additional techniques to optimize the IP WAN. These include:
— Buffering - To regulate data flow and smooth the inherent
burstiness of storage traffic, enable a large (256 megabyte)
transmit buffer for each long-link port.
— Flow control - In conjunction with buffering, TCP and GbE
provide flow control mechanisms.
TCP provides sliding-window, end-to-end flow control at the
transport layer (IP does not provide network layer flow
control). However, the TCP flow control mechanism is
inefficient and requires retransmits.
If the IEEE 802.3x Ethernet flow control standard is enabled
by GbE switches in an extended-distance link, SAN routers
negotiate the use of flow control with these switches.
Whenever possible, the best practice is to use IEEE 802.3x
flow control to relieve input buffer congestion.
— Data compression - Enable a compression algorithm to ensure
data is compact and efficiently transmitted. The data
compression ratio is a function of the data itself. Most data
streams are compressible from between 2:1 and 15:1.
— Jumbo frames - To prevent fragmentation of Fibre Channel
frames into multiple IP datagrams, enable jumbo frames to
increase the data packet size from 1,500 bytes to
approximately 9,000 bytes. Ensure the technology is
supported by all IP network equipment in the data link.
Implementing SAN Internetworking Solutions
Implementing SAN Internetworking Solutions
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