If your definition of computer storage does not go beyond simplicity, flexibility, and cost measures, you could be looking out for something that suits your environment and provides predictable performance. We have extensively looked at the Network-Attached Storage drives and seen just how much it means to have one, but we ought to figure out what Direct-Attached Storage (DAS) could be to your usage.
What is Direct-Attached Storage (DAS)?
Direct-attached storage (DAS) is computer data storage that is connected directly to the computer accessing it, such as a PC or server, as opposed to storage that is accessed over a computer network, such as network-attached storage. For individual computer users, DAS comes in the form of a hard drive or solid-state drive. DAS can be deployed inside a server chassis or as an external storage enclosure directly connected to a card plugged into the internal bus of a server. The term “Direct-Attached Storage (DAS)” is a retronym for Storage Area Network (SAN) and Network-Attached Storage (NAS).
How Does Direct-Attached Storage (DAS) Work?
Almost every PC uses direct-attached storage in the form of one or more internal storage drives, which may be traditional hard disk drives or faster solid-state drives (SSDs), typically connected using a Serial Advanced Technology Attachment (SATA) interface.
Many servers are also equipped with internal storage drives, which may be connected using SATA, faster Small Computer System Interface (SCSI), Serial-Attached SCSI (SAS), or other high-speed interfaces for better storage performance.
But direct-attached storage does not have to be connected to a computer system internally. It also includes external drives or drive enclosures (which may contain multiple drives), typically connected using USB, eSATA, SAS, or SCSI to an individual computer system.
The defining feature of all direct-attached storage is that it is controlled by a single computer to which is attached. That means that any other computer that needs to access the data stored on direct-attached storage has to communicate with the computer it is attached to, rather than being able to access the data directly.
Type of DAS
Direct-Attached Storage (DAS) is classified into 2 types viz. Internal DAS or External DAS. This classification is done based on the location of the storage device.
Internal DAS: In internal DAS design, the storage device is internally connected to the server by a serial or parallel bus. For high-speed connectivity over a shorter distance, a physical bus is used and this is also one of the disadvantages of the physical bus. Also, most internal buses can support only a limited number of devices, and they occupy a large amount of space inside the server, making maintenance of other components difficult.
External DAS: In external DAS design, the server is associated directly with the external storage device. In most cases, the connection between the server and the storage device happens over Small Computer System Interface (SCSI) or Fibre Channel protocol (FCP).
Why use a DAS for storage?
A few advantages of Direct-Attached Storage (DAS) include:
- High Performance: DAS offers fast access to data because it is attached to the computer that is requesting and consuming the data. Since it’s not connected to the network, data read/write access is fast and requests are not affected by network congestion or connectivity issues.
- Easy Setup: DAS is simple to set up, configure, and access. Since computers and servers are typically purchased with internal direct-attached storage, it is available for immediate use without configuration. External DAS devices are usually “plug and play”, attached via a USB port, and can be used as soon as they are plugged in.
- Low Cost: DAS is very cost-efficient when compared to NAS and SAN, which require hardware and software to run and manage the storage system. You only need to purchase the disk drives and drive enclosures as needed.
Limitation of Direct-Attached Storage (DAS)
Direct-attached storage does have its challenges though.
- No central management and backup: While it’s not a problem for individuals or only a few computers using DAS, growing organizations may run into problems ensuring that the data stored on DAS is available and backed up. Availability and reliability become more complicated and costly than arranging redundancy and backups on networked storage devices.
- Poor performance possibility: DAS connected to a PC can be slow to share data with other computers on a network. This is due to performance depending on the resources of the host PC. However, the issue is less prevalent when DAS is connected to powerful servers dedicated to storage.
- Limited scalability: Unlike software-defined storage that has unlimited storage, DAS is difficult to scale because the number of internal drive bays, availability of external ports, and capacity of external DAS is limited. If internal DAS needs to be upgraded, the host computer may need to be shut down during the upgrade.
Multiple factors can affect the security of DAS devices. Insufficiently managed user permissions can allow access to unauthorized users while blocking true users from access. Missing security patches and misconfigured systems can lead to open vulnerabilities.
It’s good practice to regularly run audits of user permissions, scan the DAS for unstructured information, and to keep up with the operating system (OS) and software patches.