SAN School Quiz 2 Answer # 9

• Published: 08 Jan 2004

Question #9

ISL stands for:

a.Inter switch link.
b. Isolated structured link.
c. Interoperable and scalable link.
d. Incredibly secure link.

Were you correct? The correct answer is
a. Inter switch link.

Learn more:

Switches are used to create the "fabric" part of a SAN fabric. The reason we use switches in a SAN is to create a network so the expensive storage resources like disk arrays and tape libraries can be shared between many servers.

Storage arrays have a limited number of physical ports. If we connected every server directly to a storage port (this can be done) it would limit the total number of servers that could share the storage inside the array. Hooking up one physical storage port to a 16-port switch, allows you to connect up to 15 servers to that single physical port. This way, a single port can provide storage for many servers. This is known as the "fan-in-ratio" of the port. Figuring out how many servers should share a single port is an art in itself. Some storage vendors limit you to 16 or less. Some let you connect up to 128 servers per port.

Related articles:
 

• Feature/function matrix: 2G bit/sec. fabric switches
  
• SAN scalability, part 1: Account for fabric reconfigurations in the SAN
  
• Why haven't FC HBAs followed FC switch price declines?
  
• Maximize locality when setting up a SAN

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