Network-attached storage
There are some times that you just need to throw storage on the network, accessible by a number of users, and call it a day. Enter network-attached storage (NAS). NAS installation is usually very simple. Like DAS, though, you need to answer some basic questions about how much storage you need for your particular task. Unlike DAS, NAS devices can usually be more easily expanded in the event you need additional capacity. For example, where a commonly available DAS device tops on in the 2-TB range, some NAS devices on the market can scale upwards of 200 TB. With a few exceptions, a NAS unit is a perfect device for situations where you just need to throw storage at a problem.
There are a couple of major exceptions to this rule of thumb: Most importantly, situations in which block-level access to data is required, such as for databases and Exchange information stores, are not appropriate for NAS units. Some NAS units do support these processes, but it's a case of forcing a tool into being appropriate for a job. Second, when you really need high-speed access to storage from a server, a NAS may not be appropriate since all data needs to traverse the network and is thus limited by the speed of your network.
There are two situations in which NAS devices really shine: first and foremost, Web serving, and in a very close second, general file storage. Both applications require significant disk space, but direct data access from a server is seldom required. Instead, since most data from these two types of stores is accessed over the network anyway, it doesn't matter that it's coming from a NAS vs. DAS hardware.
There's also another reason that NAS devices are really good for Web and file serving, but not for databases and Exchange stores. It has to do with what's called file-level vs. block-level data access. In file-level systems, data is accessed by a file name, as the name implies. In block-level systems, data is accessed using a block address, which is the location in which specific data is stored. In a client/server scenario, when you request a file from a file server, you're asking for a specific file and the server does the block read to get that data for you. Databases and Exchange stores have difficulty communicating in this way, so their stores are not appropriately stored on a NAS device. Databases and Exchange stores are more efficiently accessed using block-level functions available with DAS and SAN solutions.
Even though NAS is a great solution when you need to throw storage at a problem, it does have some drawbacks:
- It can be more expensive than similar DAS space.
- Not appropriate for some high-usage tasks like databases and Exchange stores.
- Data retrieval is only as fast as the network connecting the unit.
- A potential single point of failure in the storage infrastructure.
Direct-attached Storage | Network-attached Storage
Storage-Area Networks
