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I'm trying to wrap my head around how a SAN works and how it is implemented.

If I understand this well, clients wanting to access the storage devices in a SAN need to communicate with the servers via the LAN. When the SAN is implemented with Fibre Channel, these servers are Fibre Channel compliant devices, and internally in the SAN they work with the Fibre Channel Protocol. Both data and communications are supported by Fibre Channel.

But which application-layer protocol do the clients use in the LAN to communicate with the servers? Is the data simply transferred via ethernet as well? This is some part I am stuck on. I went trough a lot of sources but most sources don't really mention protocols and if they do, they only mention FCP.

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closed as off topic by adaptr, MadHatter, Chopper3, mdpc, Ward Nov 5 '12 at 18:29

Questions on Server Fault are expected to relate to server, networking, or related infrastructure administration within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.If this question can be reworded to fit the rules in the help center, please edit the question.

Starting you wholly off-topic question with "I have to write this essay" is a surefire way to get it removed... – adaptr Nov 5 '12 at 15:37
@adaptr Is there another Stack Exchange site where this belongs? Seems that Stack Overflow and Super User are out of the question... Also I just mention the essay as an introduction to where my question comes from. Question itself has nothing to do with that. – MDeSchaepmeester Nov 5 '12 at 15:39
This is off-topic, but I assume by SAN over LAN you mean iscsi (the defacto protocol for ethernet-presented block-level access to storage) If so it uses TCP, details of which after a (not very) lengthy google are available on wikipedia here – Alex Berry Nov 5 '12 at 15:40
Server Fault is really only for professional sysadmins, which you really aren't based on your original question. I've edited out the parts that might make people vote to close this, though. :) – MDMarra Nov 5 '12 at 15:45
@MDMarra as a student, of course I'm not a professional sysadmin. Since on Stack Overflow, users with any level of experience and knowledge are welcome to ask questions, I thought I could just come here with my question. Thanks for the help. – MDeSchaepmeester Nov 5 '12 at 15:48
up vote 4 down vote accepted

But which application-layer protocol do the clients use in the LAN to communicate with the servers? Is the data simply transferred via ethernet as well?

Clients don't care how the storage is presented to the servers. If it's FCP, iSCSI, or whatever on the server, it's just a block device to the server and can be presented to the clients however you want to. You can present it to clients with SMB/CIFS, NFS (gross), as a store for a website that they access via HTTP, etc etc.

The clients don't need to know and don't care how the storage is presented to the server. They have no idea if the server has FC-presented disks, iSCSI-presented disks, or local SAS disks.

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Your answer surely broadened my insight, how simple it actually is. I guess I just was looking too hard and I forgot that data should not necessarily be represented as a browsable file system to the clients. Thank you! – MDeSchaepmeester Nov 5 '12 at 15:43
Lets take a file server. In a typical Windows scenerio you have: [server]<---SMB--->[client]. With a SAN, you would have [SAN]<--FCP-->[Server]<--SMB-->Client. Hope that makes sense. It doesn't look the prettiest in a comment. – MDMarra Nov 5 '12 at 15:47
That is totally clear. And if it's a webserver, it could be [SAN]<--FCP-->[Server]<--FTP-->[Client] for example. or HTTP instead of FTP for requests. I get it. Thanks. – MDeSchaepmeester Nov 5 '12 at 15:50
Yeah, exactly. Once a block-level device like a SAN volume is presented to a server, the server can treat is just the same as any local disk. You can share all or part of it, you can make part or all of it available as a website, or anything else. Block storage is block storage, which is why centralizing disks in a SAN is such an attractive thing. – MDMarra Nov 5 '12 at 15:52

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