DAS the stuff: 5 RAID units tested

It's affordable and easy to manage--two qualities you rarely hear mentioned about storage.

It's affordable and easy to manage--two qualities you rarely hear mentioned about storage.

Direct attached storage (DAS) is one of the most basic types of storage you can get. As the name suggests, the disk storage is connected directly to the server via some type of high-speed interface such as SCSI or Fibre Channel.

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 to 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.

    Read our review of five RAID solutions in CNETAsia. Or click on the following links for individual reviews: Adaptec SANbloc, HP Modular Smart Array, Nexsan ATABeast, Promise VTrack 15100 and EMC iClariion AX100. In the article, we also explain interconnect standards like Fibre Channel and RAID specifications that you find in the RAID drives tested.