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I am from a software background so I am not really up to date with these storage technology.

I am asked this question today and I don't feel like I am able to give a correct answer.

Here is my understanding:

  • SAN refers to a set of low level of technology which ensures high availability of data storage.

  • NAS is a more generic term which refers to any device that provides access to storage over a network.

Are they correct? Did I miss any key features?

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3 Answers

up vote 2 down vote accepted

The general difference between SAN and NAS is that SAN is block level (In other words the device accessing the remote storage assigns a file system to the drive) and that NAS is file level (The device hosting the NAS provides a file system for the drive and the device accessing the remote device sees them through a protocol such as NFS or CIFS/SMB.) SANs will be faster, generally, due to the effects of transmitting block-level information instead of file-level information.

There are other things that are implied with the name "Storage Area Network" or SAN, but high availability isn't a requirement of them. Again, generally speaking if someone is talking about a SAN, they are referring to a drive or group of drives that are available at the block level through iSCSI, FC or FCoE, while someone speaking of a NAS will be speaking of a fileserver such as a linux box that is running NFS and Samba with the file system written by the hosting device.

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SANs don't have to be block level, and NAS's don't have to be file level. We have a NAS at work that is providing both block and file level services at the same time. Because it is connected to our general LAN it cannot be called a SAN device at this time. –  BeowulfNode42 Feb 22 at 2:33
    
en.wikipedia.org/wiki/Storage_area_network en.wikipedia.org/wiki/Network-attached_storage Again, SAN = Block Level, NAS = File Level. –  George Spiceland Feb 22 at 20:57
    
Note that wiki article cites no sources for those initial lines. As an example, what would you call an ethernet network that exclusively hosts storage devices providing block level access to files on the device presented as a storage LUN with iSCSI to their targets? is that network a SAN even though files are used? because the device is providing block level access via iSCSI to a LUN is it not a NAS? Things get even murkier when you introduce the notion of VLANs. –  BeowulfNode42 Feb 23 at 8:47
    
Look, I understand that the terms are more involved, but the reality is that a SAN is block level by consensus. You don't need a technical citation to answer the question "in layman's terms" so I find it beyond ironic that we're avoiding answering the question by giving absolutely incorrect information. If you walk into ANY DC and ask the most junior DC tech there what the difference between SAN and NAS is, he will tell you that SAN is block level, NAS is file level. So will any google search. It's sad to me that my answer is beneath one that is factually wrong. :-\ –  George Spiceland Feb 25 at 7:23
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forget all the fancy wording and specific cases like FC, FoE, iSCSI, etc.

SAN is a network (real or virtual, ethernet, fiber, or homing pigeon) exclusively for providing and using data storage. Though people also use SAN for the storage devices connected to a SAN too.

NAS is a storage device connected to a network that also does other things.

You can buy a "NAS box" and connect it to a SAN, so the NAS becomes a SAN device.

Think outside the box: If you had a station wagon used exclusively for transporting disks, tapes, etc with data on them you could call that a SAN with sneakernet connectivity.

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NAS can be more than one device. "Network Attached Storage" could consist of a hundred RedHat servers with massive disk arrays all of them formatted in linux file system running NFS and SMB/CIFS. It can also have a totally exclusive network specifically for Data, you don't have to use VM or production traffic networks for Data with a NAS. SANs are different altogether, SANs are huge arrays of disks that are being shared onto the network at the block level, providing "connected-as-if-directly" style attachment to the device using them. iSCSI emulates a disk connected over a SCSI connection. –  George Spiceland Feb 22 at 20:59
    
NAS can be more than one device. SANs do not have to be enormous arrays, even though they typically are. You can make a SAN out of a single switch, a 1 disk NAS, and a server with one of its multiple ethernet ports that is used exclusively for this network such as the 2nd nic on an HP Proliant Gen8 Microserver. To make the server useful and connected to other stuff another switch must be used for that network and traffic. –  BeowulfNode42 Feb 23 at 8:53
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NAS- cheap, slow shared storage over shared network

SAN- expensive, fast storage over dedicated network

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This is typically the case, but not required. I believe this is normally true because the people who are going to pay for a dedicated network for storage are going to also be paying for more expensive, bigger, faster storage too. –  BeowulfNode42 Feb 23 at 9:01
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