EMC Connectrix EC-1200 Planning Manual page 66

Fibre Channel Switching Concepts
2
Consider using multiple ISL connections to increase the total
bandwidth available for data transfer between two switches in a
fabric. Be aware, however, that increasing the number of ISLs
decreases the number of port connections available to end-devices.
Currently, the tested and supported maximum is 8 ISLs between
domains (800 MB/s full duplex). (EMC is testing higher ISL counts.
Contact EMC Customer Support for the latest guidelines.)
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Connectrix v6.02 Planning Guide