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DAS & NAS
This TekSpek covers DAS and NAS, what they mean, what they’re used for and how they’re different. We’ll start by looking at the technology, then move on to the players in the market and how the market is moving forward.
DAS stands for Direct Attached Storage and NAS for Network Attached Storage. Both acronyms signify a device that provides a means of giving a user or users more storage space, but the way they go about providing this storage is different.
The difference between the two is fairly easy to ascertain from the names, but here it is, just for clarification. A DAS device connects directly to a computer, via an interface like eSATA, SCSI or Firewire. NAS devices have a network interface of some form.
In its simplest form, a DAS device is an external drive enclosure. Plug it in to a PC and the files on the storage device are accessible through the Operating System’s file manager.
A NAS device can usually be accessed in a number of different ways. It must have some form of server running on it, be that simple windows file sharing, some form of networked file system, an FTP server, web server, or something else. Regardless of the services running on the device, it will need to be accessed through its IP address or network name (much like any computer on a network). Sometimes, zero configuration utilities are used, so that devices can be found an accessed without knowing anything about them beforehand. Connecting to a public wireless access point by using Windows or some other utility to find it is another example of zero configuration.
The actual storage subsystem of a NAS or DAS device can vary greatly, but the majority of the time hard drives will be involved. There may be just one hard drive, or there might be several, configured in a RAID mode to provide extra speed and data protection. The devices may have external connectors for the attachment of other forms of storage, such as USB drives and memory cards, which can then be copied across onto the device.
The direct attached nature of a DAS device will in some circumstances make it a cheaper option, as it isn’t acting as a standalone computer, thus it doesn’t need its own processor, memory and so on. The ‘host’ computer does most of the work. However, NAS devices need their own CPU, memory, Operating System etc. This means greater cost, or slower operation at the same price as a DAS device.
The speed of such devices depends on a variety of things. For DAS it can depend on the interface in use. For NAS, the network capabilities and the processing power of the device itself are both factors. For both, disk drive performance can also be a limiting factor. It’s not possible to generalize and say that DAS is faster than NAS, or the opposite.
If the DAS device is attached to a computer that is a server, then in theory, the storage of the DAS device could be used much like a NAS device. Of course, the DAS device depends on the setup and configuration of the server, whereas a NAS device can run just fine on its own.
Names in the NAS & DAS market include everything from system integrators, tier one companies down to companies you’d associate with providing much cheaper hardware. The demands upon a NAS/DAS system varies depending on the number of users and the environment, so companies like Sun and Dell provide enterprise and large businesses with their solutions.
At the consumer and small-business end of the spectrum are more familiar names, such as Freecom, Maxtor and Lacie. Thecus and Synology both produce NAS devices that provide multiple services, such as FTP, photo albums and so on.
Cheaper NAS devices tend to run on a Linux-based Operating System or something similar. As such, a number of services can be delivered at minimum cost to the company selling the hardware. As a result, one trend is for manufacturers to ship devices as “7-in-1” or similar, meaning they provide numerous services. Hardware limitations might make these services slow, or restricted, however.
Some NAS and DAS devices come with hard drives pre-installed. However, it’s not uncommon to buy a barebones device and fit your own hard drives. Also, it’s often easy to upgrade the hard drives. Disk space is probably the fastest growing part of such devices, so if you really need to keep up, but don’t need a new NAS/DAS appliance; you might be able to perform an upgrade.
1Gbps network interfaces are the norm these days, and most networks still operate at 100Mbps. WiFi capable devices also exist, and as new WiFi standards are introduced, so are new NAS/DAS boxes.
In summary: When choosing a device, decide whether it needs to
be network or direct attached. Then decide whether you need RAID
support. Next, look at the features you need. Finally, find a device
that can provide the level of storage you need at a price that suits