DAS is a type of storage that is connected directly to the server which enables quick access to the data but only through the server.
A network storage system helps organize and save critical information created on a computer in an efficient and accessible manner. Direct Attached Storage is an extremely versatile dedicated solution that addresses many storage problems. Its most common uses are server expansion and low-cost clustering. Direct-attached storage, or DAS, is the most basic level of storage, in which storage devices are part of the host computer, as with drives, or directly connected to a single server, as with RAID arrays or tape libraries. Network workstations must therefore access the server in order to connect to the storage device. This is in contrast to networked storage such as NAS and SAN, which are connected to workstations and servers over a network. As the first widely popular storage model, DAS products still comprise a large majority of the installed base of storage systems in today's IT infrastructures.
Although the competition of networked storage is growing at a faster rate than ever but direct-attached storage, is still a viable option by virtue of being simple to deploy and having a lower initial cost when compared to networked storage. In order for clients on the network to access the storage device in the DAS model, they must be able to access the server it is connected to. If the server is down or experiencing problems, it will have a direct impact on users' ability to store and access data. In addition to storing and retrieving files, the server also bears the load of processing applications such as e-mail and databases. Network bottlenecks and slowdowns in data availability may occur as server bandwidth is consumed by applications, especially if there is a lot of data being shared from workstation to workstation.
DAS is ideal for small businesses or departments and workgroups that do not need to share information over long distances or across an enterprise and localize file sharing in environments with a single server or a few servers. Small companies traditionally utilize DAS for file serving and e-mail, while larger enterprises may leverage DAS in a mixed storage environment that likely includes NAS and SAN. DAS also offers ease of management and administration in this scenario, since it can be managed using the network operating system of the attached server. However, management complexity can escalate quickly with the addition of new servers, since storage for each server must be administered separately.
From an economical perspective DAS is a cost-effective storage solution for small enterprises though limited in its scalability. It is ideal for setups that rely on localized file sharing and there is no need to transfer files over long distances. Enterprises that begin with DAS but later shift to networked solutions can use DAS to store less critical data. A single enclosure DAS offers some advantages – these include an easy to manage connection that can be managed with minimal skills. This is because the cabling is an integral part of the cabinet with the server. DAS is a general-purpose solution for all types of storage processing.
Organizations that do eventually transition to networked storage can protect their investment in legacy DAS. One option is to place it on the network via bridge devices, which allows current storage resources to be used in a networked infrastructure without incurring the immediate costs of networked storage. Once the transition is made, DAS can still be used locally to store less critical data.
With so many plus points, it has some drawbacks like, a single enclosure DAS design include poor scalability and limited disk capacity. This means that DAS cannot be used as the only storage medium for an enterprise environment. Poor scalability adds to the complexities in managing the storage environment. DAS does not allow for good management practices where a single data repository image is maintained. DAS does not provide the uptime or security that is associated with a SAN or NAS configuration. Disk consolidation with DAS is not feasible.
A multiple external enclosure DAS design offers the advantage of speedier recovery in case complete server hardware takes place. Storage capacity is in terabytes and greater than the internal capacity of a computer. On the flip side, a multiple external enclosure DAS adds to the complexity of management; it is more expensive than an internal solution and has greater space requirements. When setting up DAS, the following aspects regarding hard disks should be taken into consideration – disk capacity, disk I/O, and hard disk connectivity.
Large-scale DAS deployments can be a little difficult to secure because of the distributed nature of the servers. DAS security includes server security policies and access limitations to the server – both physical and over a network. DAS hosted on Windows servers can be made secure by using group policies. DAS scores well on the manageability front so long as scalability is not an issue. Backup and recovery of DAS storage can be done over LAN; but this adds to the LAN traffic and can slow down applications. A solution is to add another network to be used solely for backup and recovery but such a solution adds to the management complexity and may not be adequate for very large databases.
With DAS, redundancy is provided at the disk or controller level because with locally attached storage the fault tolerance is taken care of by localized DAS technologies. System-level redundancies cost more and in the event of a server problem the attached storage may be unavailable to users. In order to improve data accessibility the Windows Cluster service can be deployed to provide redundant hosts that share the storage subsystem. RAID configurations also add to the redundancy.
In terms of performance DAS storage delivers well because the processor and disk are situated close to each other. Any effort to scale DAS can result in performance levels falling because the storage and applications share the same set of resources. Unlike NAS and SAN which use dedicated resources for storage processing, DAS affects the LAN passage because of storage-related traffic.
Like all industries, storage networking is in a constant state of change. It's easy to fall into the trap of choosing the emerging or disruptive storage technology at the time. But the best chance for success comes with choosing a solution that is cost-correct and provides long term investment protection for your organization. Digital assets will only continue to grow in the future. Make sure your storage infrastructure is conducive to cost-effective expansion and scalability. It is also important to implement technologies that are based on open industry standards, which will minimize interoperability concerns as you expand your network.
A DAS is a dedicated storage device that's added to your environment. It's an ideal solution for applications requiring a lower-cost, entry-level cluster to maintain availability. And if a person is simply looking for an economical way to expand storage, than DAS is a smart alternative.
Scalable On-demand: highly scalable, whether to add
146GB or 10TB, disks can be added as per need them
Flexible: multiple configuration options for a variety of storage needs including transactional databases, media downloads and archiving
Dedicated: dedicated solution ensures only one accessing data on drives and can help satisfy requirements for certain compliance programs
Easy: adding a DAS is easy on budget and eliminates the complexities of growing storage by adding another server to your configuration.
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