XII Comparing SAN and NAS
Both SAN and NAS (system area networks and network attached storage) allow for sharing disk storage among multiple systems. This allows for fault tolerance and redundancy of entire systems
Network attached storage allows for a simpler appliance approach to shared storage. Off-the-shelf applications can access storage on a NAS device as if it were any other file server on the network. Users can attach to NAS-shared disk using familiar tools, such as the Windows Map Drive option, and the Linux mount command.
This plug and play approach to shared storage doesnt necessarily lead to the best solution in all situations, though. Applications may have performance requirements that exceed what NAS can provide, which can be met by a SAN solution. Additionally, some applications, notably database applications, do not tend to work well with the industry-standard file server protocols used for file access via NAS devices like NFS (Linux) or Windows File Sharing.
For example, Microsoft has a relatively-hidden technote recommending against storing Access databases on mapped drives, due to the potential for file corruption and application errors that can result when a client workstation makes changes to a database accessed via Windows file sharing, which is more meant for sharing entire Word documents and spreadsheets than database records.
If the application supports system area networks, though, you can use the SAN approach to share disk among multiple servers without concern for the kind of errors that result when using traditional network file sharing technologies. Fault tolerance and server availability may be improved by use of SAN technology, because SANs can share additional resources beyond disk, like RAM and CPUs. In many cases, one SAN server can take over for another practically seamlessly, whereas in NAS-based solutions, client reconfiguration may be necessary to cause clients to access an alternate server.
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