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What Is Direct Attached Storage (DAS) and How Does It Work?

Direct-attached storage, or DAS, is a digital storage system that connects directly to a personal computer, workstation, or server, but is not attached to a network. Because DAS is connected to only one computer or server (though it can be internal or external), it is not accessible to other computers unless they connect to it through the host computer.

Forms of direct-attached storage include hard drives and solid-state drives (SSD), optical devices such as CDs and DVDs, and tape storage.

What is DAS used for?

DAS is typically used for internal storage in personal computers and servers in the form of a hard disk drive (HDD) or solid-state drive (SSD) directly connected to the motherboard. External storage such as USB (Universal Serial Bus) devices and external hard drives are also considered to be direct-attached storage devices. 

DAS can be used as file servers in small and medium-sized businesses (SMBs) and in data centers as private storage connected to dedicated servers. Larger enterprises sometimes use DAS with networked storage systems like SAN and NAS.

DAS is used when high performance and large amounts of storage capacity are needed; it’s a practical storage choice for SMBs that need simple storage systems and don’t need to share data across the organization. External DAS can be expanded at a low cost when compared to other storage solutions like SAN and NAS.

Why is it called DAS?

Direct-attached storage is called DAS because it is directly attached to the computer or server, meaning that the storage can only be accessed by the device that it is connected to and not over a network. A DAS system can comprise hard disk drives or SSDs inside a personal computer or server chassis or an external storage enclosure connected to a server.

DAS can also refer to groups of external drives directly connected to a server using SATA (Serial Advanced Technology Attachment), SCSI (Small Computer System Interface), SAS (Serial-Attached SCSI), or FC (Fibre Channel).

DAS does not connect to the network through Ethernet or Fibre Channel or use network devices such as hubs, switches, or routers to make storage available.

How does DAS work?

DAS can be internal or external, and does not require a network connection to attach to the host computer or server. Internal DAS can be a storage device attached internally to a server or personal computer using a high-speed host bus adapter (HBA). 

Every personal computer comes with at least one internal DAS drive, which can be a traditional HDD or the faster SSD connected using a SATA interface. Servers also carry internal storage, which can be connected using SATA or other high-speed interfaces, such as SCSI or SAS.

Examples of external DAS include external hard drives and drive enclosures which can contain multiple drives. These are connected to servers and workstations using USB, eSATA, SAS, or SCSI.

DAS is managed and controlled by the computer it is connected to. Computers on the network must communicate with the computer to which the DAS is attached, rather than access the data directly.

Why use a DAS for storage?

A few advantages of direct-attached storage 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 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.

When should you use DAS?

The following are two use cases where DAS may be appropriate:

Use Case #1: Budget Constraints 

A DAS solution is less expensive than alternative network storage solutions like SAN or NAS, which can run into the hundreds, thousands, or millions of dollars. DAS is a cost-effective storage option for small and medium-sized businesses that need a lot of storage, but don’t have the budget for advanced storage solutions. 

To set up a DAS system, all you need to purchase are the required storage devices and the optional enclosures. Additional storage can easily be purchased and installed when necessary.

Use Case #2: Simple Storage Solution

DAS is also a good option for organizations that don’t have large network setups or that don’t need to share information across the organization. For these companies, DAS is a simple storage solution that’s easy to set up and requires little to no IT support. 

What are the best DAS solutions?

The best DAS solution is the one that suits your business needs, whether that’s a DAS setup with a single drive or a RAID configuration using a high-speed SAS interface.

An ideal DAS solution is designed for high-level redundancy and performance. For increased scalability, it should support multiple hard disk drives to expand storage capacity, RAID with redundant hardware components, and flash storage arrays. Flash storage is many times faster than hard disk drives, with over 100 times the read IOPS (input-output per second) and 10 times the write IOPS.

How much does DAS cost?

Generally speaking, the cost of setting up and maintaining a DAS solution is considerably less than a networked storage solution. Costs can range from around $600 for a couple of 2TB SSD drives and a RAID-supported enclosure, to thousands of dollars for a high-performance, high-capacity commercial solution.

Pure FlashArray//C for Optimal Capacity and Performance

For businesses with simple data sharing needs, DAS delivers high capacity, performance, and reliability at a relatively low price. But as your workload increases past performance and capacity limits, you’ll want to move to a more modern storage solution. 

Pure Storage FlashArray™ leverages the unique characteristics of flash storage, with FlashArray//C offering a cost-effective, capacity-oriented solution that lets you say good-bye to hard disk drives and other direct-attached storage. Even better, FlashArray//C is capacity-optimized for Tier 2 applications such as email, file and print, data backups, and archives.

For optimal storage capacity and performance, take a look at Pure Storage FlashArray//C.

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