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SAN interconnection

Posted on 2010-08-27
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Within a SAN, how are hubs, switches and bridges used. I am trying to understand the differences between them.
Thank you,
JohnD
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Question by:johndarby
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Duncan Meyers earned 500 total points
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First up: a SAN is a Storage Area Network - it is also called a Fabric. Storage arrays are often called SANs incorrectly - the SAN is the the switched network itself.

Hubs are not used in a SAN - only Fibre Channel switches. Bridges are not the same as an Ethernet bridge - you'd use a bridge to connect a native SCSI device such as a tape drive to a SAN. There is a similar construct to a hub in an arbitrated loop (similar to the old token ring network), but that's a technology that is no longer in use. The switched fabric has replaced the arbitrated loop in storage networking
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by:johndarby
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Thanks meyersd...I was aware of 3 types of "SAN" in looking across EMC, Netapp, Brocade and a few other websites: P2P 2-node, Arbitrated Loop 128-node max and Fabric 16 Million node max. I suspect you are indicating the most widely used SAN setup is a Fabric?

A good point I appreciate is the "SAN" is the switched network, itself. Thanks for that!

In some of the diagrams I saw, I noticed the terms Hub, Switch, Director Switch and Bridge. Maybe there are only 2 categories of interconnecting devices? Switch and Bridge...and as you noted in your last statement, " switched fabric has replaced the arbitrated loop in storage networking."

If you have a suggestion for a website or book that does a good drill-down into the minutiae, I would appreciate your suggestion.

Thanks!
JohnD

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by:johndarby
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Thanks so much!
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by:Duncan Meyers
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Thanks! Glad I could help.

>P2P 2-node, Arbitrated Loop 128-node max and Fabric 16 Million node max. I suspect you are indicating the most widely used SAN setup is a Fabric?
That's correct. You'd be hard-pressed to find any arbitrated loop stuff out there these  days (except for some older array internal connectivity to drives).

A switch and a director switch are pretty much the same thing with the director offering a higher level of availability and scalability. Bridges are becoming increasingly rare as most tape drive manufacturers offer FC connectivity straight to the drive as an option.

There's some good stuff available here: http://www.snia.org/education/ and here: http://www.iol.unh.edu/ and here: http://hsi.web.cern.ch/HSI/fcs/fcs.html

Happy reading!
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