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How does an IP host locate a server on a SAN?

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Tom Elgin
How does an IP host locate a server on a SAN?
on Jul 29, 2012 at 8:53:50 pm

In a SAN, devices are identified by their WWN. In TCP/IP, devices are identified by a MAC/IP address combination.

So, how does an IP host communicate with a server in a SAN, when the server doesn't speak IP?


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Alex Gerulaitis
Re: How does an IP host locate a server on a SAN?
on Jul 30, 2012 at 7:49:10 pm

[Tom Elgin] "In a SAN, devices are identified by their WWN."

I don't believe that's the case. WWN is used in Fibre Channel, ATA, SAS. In themselves, those aren't SANs.

[Tom Elgin] "So, how does an IP host communicate with a server in a SAN, when the server doesn't speak IP?"

You could also ask, "how does an IP host communicate with a hard disk on a server when the hard disk doesn't speak IP"?

That's what the server OS is for, and in case of SAN, a SAN management system.

SAN is a marriage of storage devices with a mechanism to allow shared access to them on a client side. (NAS and file servers - on a server side.) That mechanism is the one responsible for translating file access requests to storage I/O and back, and carry that I/O over the network. In case of iSCSI, file access requests are translated to SCSI I/O and carried over the network, and specifically, translates IP and IQN addresses to each other.

For the record, IP (TCP/IP) is not required for SAN - it can be any other networking protocol. IP just happens to be so ubiquitous, it's nearly a synonym of "networking".

Does this help?

Alex Gerulaitis
Systems Integrator
DV411 - Los Angeles, CA


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Tom Elgin
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 5:34:39 pm

Alex, thanks for the reply. You are correct. WWNs are only used in FC networks.

I was just reading about iSCSCI and learned you can carry SCSI commands over an IP network, so that answers my other question in part.

I also came across a device called a data router. It appears as if it is some type of "protocol converter", because it allows you to connect a SCSI device to an FC device in a SAN. So, if I understand it correctly, you can initiate via an IP network, but the storage array can be in a FC SAN. Does that sound right?


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Bob Zelin
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 6:04:06 pm

Tom,
I can show you how to setup an iSCSI network, if you are willing to show me some Cisco CLI stuff.

Interested ?

Bob Zelin



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Tom Elgin
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 6:35:40 pm

Hey Bob, I'm not trying to set up an iSCSI network. Just trying to understand the basics of SANs.

I'd be glad to help you out with the Cisco stuff though. Fire away.


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Alex Gerulaitis
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 7:28:21 pm

[Tom Elgin] "I also came across a device called a data router. It appears as if it is some type of "protocol converter", because it allows you to connect a SCSI device to an FC device in a SAN. So, if I understand it correctly, you can initiate via an IP network, but the storage array can be in a FC SAN. Does that sound right?"

Let's forget about about the "AN" part of "SAN" for a second.

SAS, FC, iSCSI devices are all the same in one respect: they are SCSI devices. They can't be shared without a secret sharing sauce that Bob Zelin is about to trade you for your Cisco CLI secret sauce.

Neither FC nor iSCSI define SAN. They actually have nothing to do with it. They just happened to have some properties that make them a good fit for SAN (the "AN" part - the networking and sharing part). Assume that an FC device or an iSCSI device is just a target storage device, much like a simple SATA hard disk. To share it, you have to use some sort of a layer on of it top that would allow concurrent processes to have their ways to access data, without data corruption. That layer can be SAN (management software on each client, possibly a lightweight server) or NAS (file serving OS right on top of that target storage device).

Once we establish that, the data router you mentioned becomes simply a protocol converter (with routing capabilities), like, say, e.g. from SCSI over IP to SCSI over FC and back. It has nothing to do with SAN, although, like iSCSI and FC, it can be integrated to be a part of it.

Alex Gerulaitis
Systems Integrator
DV411 - Los Angeles, CA


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Alex Gerulaitis
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 7:55:45 pm

[Alex Gerulaitis] "Neither FC nor iSCSI define SAN. They actually have nothing to do with it."

Technically that's not correct: iSCSI is a "SAN" protocol although, like FC, it's purely block-level access, and only allows direct one-on-one relationships. Nothing is shared until file-level locking is implemented.

The reason I say "technically" is because among creative professionals, SAN often equals "sharing". Since iSCSI or FC are not shared storage solutions by themselves (without that secret sauce) - they don't quite qualify as SANs for our purposes.

I hope I didn't confuse the bejesus out of you... :)

Alex Gerulaitis
Systems Integrator
DV411 - Los Angeles, CA


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Bob Zelin
Re: How does an IP host locate a server on a SAN?
on Jul 31, 2012 at 9:34:48 pm

I was just going to tell you the details of Studio Network Solutions GlobalSAN, which allows you to setup an iSCSI network very easily using a Mac Pro as a server.

I am not sure if this is the place (this forum) to ask lots of detailed CISCO questions.

Bob Zelin



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Tom Elgin
Re: How does an IP host locate a server on a SAN?
on Aug 1, 2012 at 12:27:04 am

Not a problem Bob. If you have some questions, shoot me an email. You
might also want to check out the Cisco Learning Network. It's free to join and has a very active forum.

https://learningnetwork.cisco.com/community/learning_center?view=discussion...

You can reach me at:

sanmanstorage -at- gmail -dot- com


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Tom Elgin
Re: How does an IP host locate a server on a SAN?
on Aug 1, 2012 at 3:49:58 pm

A little lol

Would it be correct to say that iSCSI and FC are the protocols that make SANs possible?
This seems to fall in with the definitions of a SAN from snia.org's web site:

"A network whose primary purpose is the transfer of data between computer systems and storage elements and among storage elements.

A SAN consists of a communication infrastructure, which provides physical connections, and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust. The term SAN is usually (but not necessarily) identified with block I/O services rather than file access services."

I just know I have a LOT to learn lol But I'll get there.


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Alex Gerulaitis
Re: How does an IP host locate a server on a SAN?
on Aug 1, 2012 at 7:10:58 pm

[Tom Elgin] "Would it be correct to say that iSCSI and FC are the protocols that make SANs possible? "

iSCSI and FC are integral parts of the vast majority of today's SANs - so yes, you could say that.


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Andrew Richards
Re: How does an IP host locate a server on a SAN?
on Aug 2, 2012 at 3:03:41 am

[Tom Elgin] "Would it be correct to say that iSCSI and FC are the protocols that make SANs possible? "

Go one layer lower- SCSI is the protocol that makes SANs possible, and iSCSI, FC and SAS all utilize it. Those can all also be switched, using Ethernet, FC, or SAS switches respectively.

Best,
Andy


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Steve Modica
Re: How does an IP host locate a server on a SAN?
on Aug 7, 2012 at 11:34:34 am

[Alex Gerulaitis] "[Tom Elgin] "In a SAN, devices are identified by their WWN."

I don't believe that's the case. WWN is used in Fibre Channel, ATA, SAS. In themselves, those aren't SANs."


The semantics involved in all this are ugly. People regularly call our NAS offering a SAN.
FIbre Channel, GSN, iSCSI, and AOE all offer "SAN". They are storage networks. Xsan, CXFS, MetaSAN, and FibreJet are all products that offer gatekeeping/sharing capability on your SAN. In and of themselves, they are not SANS.

Steve Modica
CTO, Small Tree Communications


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Steve Modica
Re: How does an IP host locate a server on a SAN?
on Aug 2, 2012 at 3:44:59 pm

I went back and read this a couple of times to understand what's being asked. A "server" on a SAN network would usually be a metadata server.

The closest I could come would be "how do iSCSI clients (which could be interpreted as part of a SAN) find their iSCSI targets (which could be interpreted as "servers"). In that case, they usually use isns (internet storage name service). Several vendors support this, but not all vendors. In most cases, people just "know" the ip address. FCoE does broadcast discovery. One of the interesting things about FCoE is it just finds and mounts everything :) So you need to segment things off with zoning. That's just the way it's done.

Steve

Steve Modica
CTO, Small Tree Communications


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Tom Elgin
Re: How does an IP host locate a server on a SAN?
on Aug 2, 2012 at 7:20:44 pm

Thanks for that info Steve. That's the first time I've ran across the term isns. Yet another acronym to memorize lol


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Alex Gerulaitis
Re: How does an IP host locate a server on a SAN?
on Aug 2, 2012 at 10:07:15 pm

[Steve Modica] "I went back and read this a couple of times to understand what's being asked."

Steve, were my answers generally on target? I only know enough to be dangerous - and would love to get a better understanding how all this stuff works.

Alex Gerulaitis
Systems Integrator
DV411 - Los Angeles, CA


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