FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Environment Planning Manual (620-000124-500, April 2005)

3
Planning Considerations for Fibre Channel Topologies
3-33
Planning Considerations for Fibre Channel Topologies
Figure 3-12 ISL Oversubscription
Two NT servers, each with maximum I/O of 100 MBps, are
contending for the bandwidth of a single ISL operating at 1.0625
Gbps. In addition to data, the ISL must also transmit Class F traffic
internal to the fabric. When operating at peak load, each NT server
receives less than half the available ISL bandwidth.
Depending on fabric performance requirements and cost, there are
several options (best practices) to solve ISL oversubscription
problems, including:
• Employ device locality - NT Server 1 and its associated storage
device can be connected through one director. NT Server 2 and its
associated storage device can be connected through the other
director. As a result, minimal traffic flows across the ISL between
directors and the congestion problem is mitigated. For additional
information, refer to Device Locality.
• Install an additional ISL - A second ISL can be installed to
balance the traffic load between fabric elements. Two ISLs are
sufficient to support the bandwidth of both NT servers operating
at peak load.
NT Server 1
(100 MBps Max)
1 Gbps ISL
Storage
NT Server 2
(100 MBps Max)
T
M
T
M
1
5
10 15
20
25
0
100
150
200
Time (Sec)
Bandwidth (MBps)
50
1 Gbps ISL
NT Server 1
NT Server 2