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This article is contributed by my esteemed colleague, Mark Henderson, Sr. Technical Marketing Manager for our E-Series product line.

 

One of the questions commonly raised about E-Series relates to SAS connectivity.  “Isn’t SAS a disk type?”  “What would you use SAS for?” and “12Gb/s just doesn’t sound that fast.”

 

SAS2.jpgSAS (Serial Attached SCSI) is a storage communications protocol and is used to describe a disk type by its interface.  And the SAS protocol is used to interconnect E-Series disk expansion shelves.  But it is also used to directly attach E-Series storage to servers.  This is perfect for small server count installations that need centralized storage.   A handful of servers can directly attach via SAS, and then they can serve the rest of the organization.   This direct attach architecture can scale and avoid the complexity, cost, management and performance overhead of a storage network.

  

Directly attaching a few servers to centralized storage also works for clustered environments where the “cookie cutter” approach is used to replicate a working group.  Some of the largest installations in the world are done in this fashion.

 

And this approach it is under marketed. 

   

Yes, I said, “under marketed”.

    

E-Series 12Gb/s SAS is actually quad-lane 12Gb/s SAS.  So an apples to apples comparison to other server network connections such as 10Gb/s iSCSI, 8Gb/s or 16Gb/s FC, would list quad-lane 12Gb/s SAS labeled as 48Gb/s SAS.  Four or more ports of that kind of speed adds up fast!  It also turns out that as an I/O protocol, SAS is very efficient when compared to encapsulating I/O inside of a FC frame or an iSCSI packet.  Couple
the speed with the inherent efficiencies of the SAS protocol and you have a connection method that can’t be beat for small numbers of servers.  And yes, SAS is just like any other connection technology and never sees full max speed all the time, but you get the idea.

 
SAS is also super easy to draw on your customer’s whiteboard!  Four boxes for servers and one cylinder for storage connected with some lines are you are done!  (You don’t even need all the colors.)

   

E-Series Direct Attached SAS: less complexity, less cost, less management and less performance overhead are more for your money! 

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