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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?

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2 Answers 2

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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?)

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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.

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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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