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What is the use-case for NAS on a mid-to-high end storage array?

SAN is block level, NAS is file level. Block level means applications access blocks,while in file level they use files.

Now, we can also create file system on server operating system for block level storage, so what is the advantage of using file level access with NAS.

Please clear my doubts and mistakes.

Community
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Drt
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4 Answers4

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When using SAN the OS and Filesystem needs to be aware that changes to the blocks can be made by several systems at one, creating possible problems on the filesystem.

Some systems can handle that (designed for this type of access) like VMware vmfs, but most (both server and client) systems are designed to be singe-access to the file-systems on a block-level => if there is only a slight chance of duplicate access you would really want to use some file-level access, which can be handled in these systems ( = multiuser) => NAS

tsg

Truebsalgeblaese
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Now, we can also create file system on server operating system for block level storage, so what is the advantage of using file level access with NAS.

  • You are not limiting yourself to cluster aware file systems, which are few and with their own problems (the problem in iteself is complex).
  • A NAS has security on file level which is pretty important for any business level file access. In a SAN you can do that on the disc level, but every machine can read the whole disc, which means you can do a disc level analysis. A NAS can regulate access on the network interface efficiently.

That pretty much is it. Generally SAN is used for

  • Single computer access (remoet boot to a volume without discs internally)
  • Backend storage (no USER goes there, only computers)

A NAS on the other hand

  • Is used for variety user access as it has better security (can filter out files people are not allowed to see) in one file system.

Technically there is not a lot different. Many SAN can serve as NAS, pretty much every NAS can also work as SAN. There is no hardware that is required for a SAN - many people think SAN is Fibre Channel controllers. THat is "old tech". Yes, theey are dominant, but they are not particularly fast either. 10G, Infiniband are better (particularly infiniband) when you can use them. This really these days is more a logical separation.

THe most important thing in many cases is the trust boundary. Even with cluster file systems - it would be utterly stupid to hand out files via a SAN when every computer can see the WHOLE SHARED DISC and then download it and try to decrypt the file system. A NAS has a defined safe api here - you ask for a file, if the NAS says it is not there, you can not access the disc to bypass this.

TomTom
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The primary advantage of NAS is that dissimilar devices can access the same filesystem at the same time.

David Schwartz
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Probably the most common file system in NAS is NFS, which can be accessed easily from several devices at the same time. There are solutions for multi-device-use also in SAN, but then you need global file system, which may be considered not that easy to set up.

grassroot
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