It's affordable and easy to manage -- two qualities you rarely hear mentioned about storage. We test your RAID options.
DAS is ideal for localised file sharing for a single or small number of servers -- the DAS is managed using the network operating system of the server it is attached to. While management and administration are initially quite simple, as the complexity increases with additional servers it becomes more difficult to manage as the storage for each server must be handled separately.
In terms of cost, DAS is very inexpensive when compared with network attached storage (NAS), however, if you are anticipating rapid growth bear in mind that DAS is limited in its scalability when compared to NAS.
Here is a list of things to look for when purchasing a DAS appliance:
- Scalability
- Fault tolerance
- RAID configurations supported
- Redundant power supplies and controllers
- Battery backup on controller cache
- Automatic failover
- Global hot spare drives
- Automatic and transparent drive rebuilding
- Management
- Remote management software
- Performance analysis and tuning tools
A few years back, if you pulled a drive from a RAID DAS unit it would have been a pretty fair bet that it would have been some flavour of SCSI. Recently, however, IDE has made strong inroads into DAS with the advent of powerful ATA RAID controllers. This has a two-fold advantage: not only are ATA drives less expensive than a similarly sized SCSI drive, ATA drives are also available in much larger capacities.
There is a downside of course. SCSI does have a higher bandwidth and is available with 15,000rpm spindle speeds compared to 7200rpm for ATA, it has shorter seek times and generally significantly longer mean time between failure (MTBF).
Another drive type that is also encroaching in the DAS space is Serial ATA (SATA), although SATA drives have similar advantages and disadvantages to the ATA.
Of the DAS units tested, the Adaptec has Fibre Channel SCSI drives, the ATABeast (as the name suggests) ATA drives, and the Promise comes with SATA drives.
