Besides the technological differences between SAN and NAS, some application vendors say their products cannot work over NAS. An example is MS Exchange. Is that really true? If so, many NAS products will be aside of some application implementations, like databases, regardless of their new high-performance achievements.
It is possible for an application to write to disk by bypassing certain file system interfaces - especially if the company making the software makes the operating system and the file system, such as Microsoft. Whether or not MS Exchange does something like this I do not know.
Another matter entirely is whether or not a product is supported using NAS (technical support, I mean). It could be that everything will work fine, but if you ever have a problem the company will tell you that you have an unsupported configuration. This is because NAS might not have a way to guarantee ordered delivery or acknowledge receipt of all I/Os. If you have a transaction-based system, these are important to maintain the integrity of the data. NFS, being stateless, has no way of providing this.
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