Unified Serial RAID Controllers for PCIe

Unified Serial Controllers Do SAS And SATA

Professional and semi-professional RAID controllers have changed considerably since the serialization of SCSI commenced. The parallel SCSI standards shared their total bandwidth of up to 320 MB/s across all devices and required daisy-chaining devices using costly and sensitive cables. In contrast, Serial Attached SCSI (SAS) supports a dedicated 300 MB/s bandwidth per port, multi-lane or individual device cables, optional redundant cabling, and internal or external device operation. Controllers are even compatible with SATA, meaning that you can mix high-capacity SATA and high performance SAS hard drives. Finally, the transition from PCI-X to PCI Express is underway. All of these reasons were enough for us to have a look at four RAID controllers for entry level servers Compare Prices on RAID Controllers.

Many people might wonder if it even makes sense to purchase a dedicated RAID controller, considering the availability of powerful integrated SATA controllers such as Intel’s ICH9R, which can be found on many upper class motherboards such as the Asus P5K-WS (P35 chipset plus PCI-X interface) or the P5K64-WS (quad PCI Express slots). Since manufacturers have been providing their top models with high-grade voltage regulators and premium components, the quality difference between a high-end desktop motherboard and a low-end server product only lies in the feature set. With six SATA/300 ports on such a motherboard, advanced RAID management software and a dual core or quad core processor to take on the workload of RAID 5 parity calculation, why still bother with a dedicated and expensive RAID controller?

Such an integrated solution will probably do for a small workgroup server to host project and user data as well as applications, but will quickly hit its limits. Once you need more sophisticated RAID levels such as RAID 50 or 60, the integrated solutions won’t be any good. If you suddenly need to attach more than six drives, you’ll be forced to switch to a different controller. Also, if you want to run your storage array in a dedicated external appliance, or if you want to manage your drives properly, then SAS, outdated SCSI solutions or proprietary solutions are your only options.

We clearly recommend against proprietary solutions that force you to get controller plus storage appliance in a bundle for the sake of management features. The article Going the SAS Storage Way provides plenty of information on Serial Attached SCSI: interface details, cables, expanders, backplanes, hard drives, host adapters, appliances and enclosures. Using the latest SAS hard drives will give you much more storage performance than SATA ever could, but cross compatibility with SATA and flexibility of use are the key reasons to go for a unified serial controller for your small business.

Join our discussion on this topic

  • Rik
    - Unless RaidCore is trying to peddle their VST Pro software,...aka as Fulcrum proprietary based ? which BTW you said no to, I don't see any advantages here.
    Why?, ZFS is free !
    And, where are the Drives for Solaris, or the xBSD's , or even MacOSX !!!?
    -and still no, becuase their newer 54xx series doesn't support the other 'ix OS's.
    Nope, unfortunately, not much to see here.
    so, based on the above, Adaptec 5805,... or Areca,... blows this.

  • aapocketz
    For SAS, the two connector segments were merged, which makes it possible to attach a SAS drive to a SATA controller using the continuous connector, but you cannot hook up a SAS hard drive to a SATA controller using the SATA connector (SFF 8482).

    I think this paragraph has an error. I believe it should read

    For SAS, the two connector segments were merged, which makes it possible to attach a SATA drive to a SAS controller using the continuous connector, but you cannot hook up a SAS hard drive to a SATA controller using the SATA connector (SFF 8482).

    In fact I believe the statement should have less emphasis on the connector as its the actual controller that appears to limit the connectivity, the connector is just keyed to allow you to plug SATA drives into SAS but not the other way around.

    from wikipedia: "SATA 3.0 Gbit/s drives may be connected to SAS backplanes, but SAS drives may not be connected to SATA backplanes."

    I believe the fact that signaling voltages are nearly double on a SAS drive is significant to mention.

    Let me know if I am wrong, I just started playing around with a bunch of SAS drives so I am figuring this out as I go.
  • Factors like spindle speed, density, latency etc. effects drive performance as much or more than bandwidth. A 300GB 2.5 15K SAS drive will smoke a 1TB 7200 SATA drive simply because it has about twice the IOPS. The bandwidth is meaningless if you can't get the data on and off the disk at the speed of the bus. Furthermore, except for the WD Velociraptor 10K+ spindle speed drives are non-existent in SATA but are prevalent in SAS. So from an interface standpoint they are very close but SAS drives are really intended for entirely different markets and applications and budgets I might add.
  • Bicom Systems
    Great article - thanks for the comparison! We also did a piece on SAS and SATA, if you're interested : http://blog.bicomsystems.com/sas-vs-sata