Storage Architecture

Direct Attached Storage

Direct Attached Storage (DAS) can take on many meanings. DAS typically refers to a storage device that is physically attached to and controlled by a server. When storage expansion is needed, simply adding additional mass storage devices is a matter of attaching it to the server. DAS is the most traditional way of expanding the storage needs of a server.

Internal Storage Expansion

PowerEdge servers can utilize multiple hard drives. Most PowerEdge hard drives have built-in carriers that make adding hard drives as simple as sliding it in an available slot. Typically the server is powered down, the hard drive installed, and the server is powered back on. During the server's POST sequence, the new hard drive will be detected. The server operating system is then used to partition and format the new drive for use.

There is however a drawback to this method. The server has been removed from production possibly resulting in user downtime. A limited number of hard drives can be added to the server.

External Storage Expansion

If a server's internal storage cannot be expanded or is not desired, then external expansion is an alternative option. A SCSI or Fibre Channel JBOD can be utilized. It attaches to the server using either SCSI controllers or HBAs. A point-to-point connection exists between the server and storage device, the server having complete control of the device.
When adding external storage, the server must also be removed from production possibly resulting in user downtime. A limited number of SCSI hard disk arrays can be added to a server due to SCSI limitations.

Tape Backup

Tape drives can be directly attached to a server either internally or externally. The tape drive is controlled by backup software. Using this arrangement, a tape drive must be installed into each and every server needing to be backed up including backup software. This could be an ideal solution for a small company, but too costly for the average enterprise.

In addition to the required hardware and software, each server is responsible for backing up its data. There is no central backup using a direct attached method.