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What is a Fibre Channel Disk within an EMC SAN?

Posted on 2010-09-08
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Last Modified: 2012-05-10

Hi

I'm confused as to what a Fibre Channel Disk is!

I understand that Fibre Channel Protocol (FCP) is a network technology similar to TCP/IP. Also, I understand that for storage, SATA or SCSI can be transported over FCP.

However, our CLARiiON SAN has two types of disks which it calls SATA and FC.

I think I understand SATA as SATA being carried over FCP.

However, is the FC disk SCSI being carried over FCP? Or is the FC disk some type of FC protocol for transferring data carried over FCP?

Finally, does FCP operate in a similar fashion to the TCP/IP stack i.e. are the SATA/SCSI command encapsulated within a FCP "packet"?

Thanks

John
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Question by:TSC70
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by:Coast-IT
ID: 33627492
I hate to quote wiki, but in this case it's the best explanation ;

http://en.wikipedia.org/wiki/Fibre_Channel_electrical_interface
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Expert Comment

by:edhorch
ID: 33627566
Think of Fiber Channel as just another disk interface like SCSI, IDE, SATA, etc..  Despite the name, FC can be used with either optical fiber or copper physical connections between the drive and the interface.  Most operating systems identify FC drives using the same notation as SCSI, i.e., {which controller, which interface, which target number, which LUN}, but in a SAN situation, physical drives don't matter--the drives a client sees are virtual and configured in the SAN, independently of the drives themselves.
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by:dlethe
ID: 33627597
A simple somewhat watered down, and purposely ambiguous enough to get point across w/o making you do a lot of reading from perspective of the EMC product is that FC & SATA represent 2 different types of disk drives that the EMC supports.  They have additional hardware to "convert" SATA physical interface so that it can plug into a FC port on their array.   Once this interposer is added (the hardware magic), the native ATA commands that a SATA disk uses are encapsulated within a SCSI command-set, which is then encapsulated within FC frames as you suspected.  (Again, not getting as deep as I could, but hopefully this is enough to get the 10,000 foot view)

This electronics makes the SATA disk appear as a FC device, so all of the wonderful EMC software can use it.  The downside is that SATA disks are slower and have less diagnostic capability. Mix and match as you desire.  SATA=cheap and slow,  FC=expensive and fast.  
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Author Comment

by:TSC70
ID: 33627663
Hi dlethe

That is very helpful!

What I still don't understand 100% is that does the FC disk still use/encapsulate the SCSI command set i.e. are they SCSI disks? Or is there an equivalent FC protocol for SCSI?

Thanks

John
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dlethe earned 500 total points
ID: 33627734
FC, SCSI, SAS drives all "speak" the SCSI command-set.   IDE/ATA/SATA disks speak the ATA command set.

Yes fibre channel is a flavor of SCSI. it is serial SCSI, the SCSI you are familiar with, that has 50/68/80 pins is parallel SCSI.  SAS disks use serial SCSI interfaces.  Don't confuse the interface type with the instruction set.  This is what throws people off.

P.S.  USB also speaks SCSI, and it is a serial interface.  And while I am at it, put a SATA disk on a SAS controller and it also speaks SCSI.   Most RAID controllers designed for ATA/SATA disks also present a SCSI device to the O/S.

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Author Comment

by:TSC70
ID: 33627803
Hi dlethe

That makes alot of sense. Thanks. The separation of SCSI as a command set and its interfaces (parallel, serial, IP, FC) clarifies things immensely.

A final query - what would be a good resource to do a bit more reading on this?

Thanks

John
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LVL 47

Expert Comment

by:dlethe
ID: 33628099
T13.org, t11.org, t10.org ...
Those are the tech sites that have ALL the specs.  I'm not up on any survey or introduction type material.  
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