I want to buy some cheaper HDs for our server (it will have practically zero HD access) but I plan to put them into a RAID 1 config, just for peace of mind. Our server is a second-hand PowerEdge 860, with a SAS 5i/R controller on it.

The existing drives (which came with the server) are Barracuda 7200.9's which are "SATA II" (i.e they've got 3Gb/s speeds and NCQ). That would answer my question except that Seagate made them to be 100% backwards compatible, too.

I'm concerned that newer, bigger disks, that may not be 1.5Gb/s backwards compatible, will not work with the SAS 5i/R controller.

Does anyone know for sure?


Speed negotiation is part of the SATA initialization protocol. Any controller worth it's weight properly implements this. Some early VIA and SiS chipsets were known to fail at this, but I would expect better from the SAS 5i/R (LSI, I believe?)

  • Yep, rebadged LSI. – womble Nov 17 '09 at 17:43
  • It is indeed an LSI (model #: UCS 51, I think). – Django Reinhardt Nov 17 '09 at 19:30
  • Confirmed. Nautilus reports negotiation at 3.0Gb/s. Woo! – Django Reinhardt Nov 19 '09 at 18:25

According to the documentation on Dell's website (link), SAS 5iR does support SATA, but doesn't explicitly say SATA I or II. Kyle Smith is right in terms of speed negotiation. Newer controllers should be able to handle speed negotiation. I'm willing to bet older controllers might require a jumper to enable it.

To answer your question: I don't think anyone knows for sure unless they've run your exact setup with the 5iR and the Seagate Barracuda 7200.9. If I were a gambler, I'd personally take the chance as SATA is fairly mature and commonplace these days.

According to Wikipedia (link), the section on "SATA 3 Gbit/s (Second generation)":

Given the importance of backward compatibility between SATA 1.5 Gbit/s controllers and SATA 3 Gbit/s devices, SATA 3 Gbit/s autonegotiation sequence is designed to fall back to SATA 1.5 Gbit/s speed when in communication with such devices. In practice, some older SATA controllers do not properly implement SATA speed negotiation. Affected systems require the user to set the SATA 3 Gbit/s peripherals to 1.5 Gbit/s mode, generally through the use of a jumper, however some drives lack this jumper. Chipsets known to have this fault include the VIA VT8237 and VT8237R southbridges, and the VIA VT6420, VT6421A and VT6421L standalone SATA controllers.[10] SiS's 760 and 964 chipsets also initially exhibited this problem, though it can be rectified with an updated SATA controller ROM.[citation needed]

Seeing as you're using the SAS 5iR and don't have to worry about the VIA/SiS chipsets, I'd be willing to try it out. Just my two cents.

  • Thanks for the link. The specs on Dell's website DO say it supports 3Gb/s transfer... not sure if that means it includes the so-called "SATA II". – Django Reinhardt Nov 17 '09 at 19:29
  • Yeah, the documentation is a bit ambiguous, but considering the controller is relatively new, I'd bet on it and say it would work with the 7200.9 Barracudas. – osij2is Nov 17 '09 at 20:00

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