Direct Attached Storage (DAS)
Das is short for Direct Attached Storage.
Direct Attached Storage (DAS), also called Direct Attach Storage, is digital storage that is attached directly to a PC or a server. In other words, DAS isn't part of a storage network. The most familiar example of DAS is the internal hard drive in a laptop or desktop PC. In practice, the term "direct attached storage" is used most often in reference to dedicated storage arrays attached directly to servers. It is used to distinguish DAS from networked storage arrangements, like SAN or NAS devices.
DAS Devices Explained
DAS can refer to a single drive or a group of drives that are connected together, as in a RAID array. In addition, DAS devices can be housed inside a PC or server (as is the case with internal hard drives) or outside the PC or server (as is the case with external hard drives and storage appliances). Multiple systems can use the same DAS device, as long as each PC or server has a separate connection to the storage device.
The primary benefits of DAS include simplicity and low cost. Installing networked storage systems, like NAS and SAN devices, requires more planning, as well as the purchase and deployment of network hardware, such as routers and switches, in addition to appropriate cabling and connections. By contrast, most PCs and many servers come with DAS already installed, and if you want to add more direct attached storage, generally all you need to purchase is a storage device and possibly a cable. Maintaining DAS is also very simple; by contrast, SAN and NAS solutions usually require management software and may require monitoring software as well.
DAS vs. SAN and NAS
In the early days of computing, DAS was the only type of storage available. In fact, the term "direct attached storage" didn't come into use until much later when people needed a way to differentiate between traditional storage and SAN and NAS devices.
NAS stands for "Network Attached Storage." It offers file-level storage for end users that are connected to a network. The advantage of NAS over DAS is that it simplifies file sharing among multiple users while potentially offering faster performance than a traditional file server.
SAN stands for "Storage Area Network." It refers to a network of storage devices that provides block-level storage for servers in a data center. For large organizations with many servers, SAN offers better performance and flexibility than DAS, along with potential cost savings, although SAN hardware can be costly.
Many SAN and NAS devices can also be used as DAS devices. The difference lies in whether they are attached directly to a server or attached to a network via routers and switches.
Recommended Reading: What is Enterprise Storage?
Setting up a DAS device is generally very simple. When you purchase a PC, DAS is included in the form of the hard drive. If you would like to add more Direct Attached Storage to a laptop or desktop, you can attach a plug-and-play external hard drive.
DAS is also included in many servers. Connecting additional DAS devices to servers is a little more complicated than adding DAS to a PC, but it is generally simpler than connecting SAN or NAS devices because it doesn't require you to design a network or purchase hardware like routers and switches. Depending on the type of server, you may be able to add DAS in the form of additional drives in your existing server chassis. Other times, DAS sits in a separate chassis. You can also purchase DAS as storage appliances that you can connect directly to your servers. DAS deployment may require some configuration, but most IT workers can handle it on their own without outside consultants or specialized technical experts.
Using DAS is very easy -- you simply save files as usual. Your operating system will allow you to view, rename, delete and perform other operations on the files on your DAS.
DAS devices can utilize traditional spinning hard disk drives or solid state media. Hard disk drives (HDDs) are less expensive than solid state drives (SDDs) on a per gigabyte basis. However, they aren't as fast as SDDs. The majority of DAS devices sold today use hard disk drives, although SSDs and hybrid devices are becoming more popular, particularly for applications where performance is paramount, such as Big Data analytics.
Conversely, SSDs offer the fastest performance, but they are also the most expensive. However, in recent years, they have become more affordable. In addition, because SSDs don't have a spinning disk, they last longer and offer better reliability than HDDs. Many vendors now offer SSDs as an option on mid- to high-end servers for part or all of the storage capacity.
DAS devices can connect to PCs and servers via a variety of protocols, including SCSI, SAS, SATA, ATA, eSATA and Fibre Channel.
Although SAN and NAS devices are growing in popularity among enterprise users, most storage vendors also offer DAS hardware. Those vendors include the following:
- Direct-Attached Storage Coming of Age in Web 2.0 World
- Implementing Backup for Your SMB
- Server Virtualization Breathes New Life Into DAS
- New Life in Old DAS
- Dell Storage Buyer's Guide
- In Support of Networked DAS