Chapter 5. Direct-Attached Storage and Introduction to SCSI
Direct-Attached Storage (DAS) is an architecture where storage connects directly to servers. Applications access data from DAS using block-level access protocols. The internal HDD of a host, tape libraries, and directly connected external HDD packs are some examples of DAS.
Although the implementation of storage networking technologies are gaining popularity, DAS has remained ideal for localized data access and sharing in environments that have a small number of servers. For example, small businesses, departments, and workgroups that do not share information across enterprises find DAS to be an appropriate solution. Medium-size companies use DAS for file serving and e-mail, while larger enterprises leverage DAS in conjunction with SAN and NAS.
This chapter details the two types of DAS along with their benefits and limitations. A major part of this chapter is devoted to detailing the types of storage devices used in DAS environments and SCSI—the most prominent protocol used in DAS.
Types of DAS
DAS is classified as internal or external, based on the location of the storage device with respect to the host.
Internal DAS
In internal DAS architectures, the storage device is internally connected to the host by a serial or parallel bus. The physical bus has distance limitations and can only be sustained over a shorter distance for high-speed connectivity. In addition, ...
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