HP P6000 Continuous Access Implementation Guide (T3680-96431, August 2012)

Table 2 (page 17) lists the intersite one-way latency inherent to other distances.
Table 2 Sample one-way latencies
Point-to-point cable distance in km (miles)One-way latency (ms)
200 (125)1
600 (375)3
1,800 (1,125)9
3,600 (2,250)18
7,200 (4,500)36
12,000 (7,500)60
20,000 (12,500) current maximum limit100
Determining intersite latency
To determine intersite latency on an existing network, use network utilities such as the ping
command. Obtain a 24-hour average. See the HP SAN Design Reference Guide for more
information about network utilities.
Evaluating intersite latency
The Data Replication Designer can be used to gather intersite latency data. The designer is supported
on Windows only. See “Tools for gathering SAN data” (page 14) for more information on the
Data Replication Designer and other tools available for evaluating intersite latency.
Cost
The cost associated with transmission lines increases with distance and bandwidth requirements.
The cost may prohibit the selection of a favorite site. If the required bandwidth proves too costly,
consider moving the remote site closer to the local site or replicating only the most critical data,
such as transaction or retransmission logs.
Choosing the intersite link
The location of the remote site determines the intersite link technologies that meet your distance
and performance requirements. Including distance, the following factors affect bandwidth:
• “Distance” (page 17)—The transmission distance supported by specific link technologies
• “Recovery point objective” (page 18)—The acceptable difference between local and remote
copies of data
• “Bandwidth capacity and peak loads” (page 18)—The effect of application peak loads on
bandwidth
Distance
HP P6000 Continuous Access supports direct Fibre Channel (FC) and extended Fibre Channel-to-IP
(FC-to-IP) links ranging in bandwidth from 2.048 Mb/s to more than 4 Gb/s. The supported
transmission distance varies with the technology.
• Basic fiber supports a maximum of 500 meters at 1 Gb/s; shorter lengths are supported at
higher bandwidths. The distance varies with the speed of the link. For more information, see
the HP SAN Design Reference Guide.
• Fiber with long-distance and very-long-distance GBICs can support up to 200 times the basic
fiber distance.
Choosing the intersite link 17