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Question using Virtual Connect Fibre Channel vs. using VC FlexFabric FlatSAN capability.

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Question using Virtual Connect Fibre Channel vs. using VC FlexFabric FlatSAN capability.

Kathleen was looking to help guide a customer:




I’ve got a customer trying to decide on a SAN design for their C7000 Enclosure.  They have the following questions:


  1. Should they use VC FlexFabric or VC -FC modules?  What are the benefits and drawbacks of both
  2. What modules do they need to do direct attach 3PAR Storage Systems?  What are the benefits and drawbacks.




Reply from a couple people:




From Dan:

Direct Attach to 3PAR at the moment is only VC FlexFabric.


FlexFabric vs VC FC


1.  Pro: FlexFabric costs less because even though the modules are more, they are cheaper than adding 2 VC FC modules and 8-16 HBAs.


2. Pro:  VC Flex-10/10D+VC-FC modules: VC-FC combined with VC Flex-10/10D modules effectively doubles the total amount of bandwidth you have on both uplinks and downlinks.  This is only a big Pro if the customer really needs that amount of bandwidth.  FF = 2x10 down and approx. 4x8 + 4x10 up.  Whereas 10+FC = 2x10 + 2x8 down and 8x8 + 7/10x10 up.


For Stacked domains, FlexFabric can run out of ports very quickly.

2 x 10Gb, 2 x 8GB FC, 2 x Horizontal Stack and 2 x Vertical stack = out of ports.



Input from Chris:

The practical issue is that in an enclosure with multiple servers you typically will have the need to connect some servers to other FC devices – other disk arrays, tape libraries, etc.  So you need FC fabrics.  Once you have them it is much easier and more flexible to connect to 3PAR through the FC fabrics.


To me a good use case for direct attach to 3PAR would be if you had a humongous UNIX server e.g. SD2 based with say 16 FC HBAs all attaching to a dedicated 3PAR.  Then it makes sense to directly attach.  The configurations like that were common in the end of the last century, but they are becoming increasingly rare.




Your comments or questions?