DAS RAID and Hot-Swap

The following scenario presents a good case for "lean infrastructure." With DAS, the first level of redundancy is typically provided by using either a software or hardware RAID-5. By using an external disk housing, the ability to hot-swap drives can be provided in case an individual drive fails. An example DAS storage configuration might be as follows:

Item

Example Model

Unit
Price

 Quantity Subtotal

80GB 7200RPM IDE (Internal OS drive, RAID-1)

Western Digital Caviar WD800BB 80GB 7200 RPM IDE Ultra ATA100

$48

 2

$96

500GB SATA 7200rpm 3Gbps Drive (Data drive, RAID-5)

Maxtor DiamondMax 11 6H500F0 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s

$325

 4

$1,300

eSATA RAID controller

Adonics ADS3GX4R5-E External 4-port eSATA II PCI-X

$109

 1

$109

Hot swappable 4-bay external drive enclosure

SeriTek/2eEN4 External eSATA Enclosure

$495

 1

$495

Total      

$2,000

In this example, a redundant pair of internal drives provide 80GB of space for the OS and applications while an external enclosure has 4-way RAID-5 with drive hot-swap, providing 1500GB of usable space for the message storage. Prices quoted are one-off retail in Feb.  2006. Note that this hardware is high-density low-cost storage and, as storage, is not particularly high performance. However, when combined with the PostPath Server™ software that has been carefully optimized to use storage efficiently, the overall resulting system is high performance. Contrast this with Exchange™, where, low-cost storage of this kind would deliver a poor performance result.

Of course, instead of specifying your own storage subsystem as above, you can also buy prepackaged direct-attached SCSI or (as above) S-ATA hot-swap disk systems from a number of server and storage vendors. Many of these prepackaged solutions also offer excellent value.