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Vincent Vancalbergh
Asked: 2011-06-21 01:35:54 +0800 CST

Nearline SAS on SATA controllers

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I know that SAS drives cannot operate on a SATA controller. I know that SATA drives can operate on a SAS controller.

But can Near-Line SAS drives, being SATA drives with a SAS controller, be used on
A) only SAS controllers
B) both SATA and SAS controllers
?

Note that the nearline SAS drives feature "dual port", but I'm unsure if this means "has a SATA and a SAS port" or "has 2 SAS ports". Especially since I seem to read that the connnectors and cables themselves seem to be interchangeable, which, if they are, would make the dual port conundrum moot.

sas sata controller

2 Answers

  1. Best Answer

    "I know that SATA drives can operate on a SAS controller" - you may know many popular SAS controllers than can run SATA disks but don't make this assumption, there's nothing in the SAS specs that state they should also run SATA disks, they just share a lot of common features (connectors/cabling etc.). Manufacturers can pick and choose to do as they wish.

    Now your question - no this won't work, it's the SAS signalling that's different, so no SATA-only controllers won't be able to work with any SAS disks at all. Also again it's an assumption of yours that all near-line drives are SATA with a SAS controller - that's not the case, it's the controller that defines the protocol used. Near-line SAS disks are just disks, there's nothing inherently SATA-oriented about them, they then have a SAS controller attached to them.

    Dual-porting is a SAS feature that allows a single disk to have two physical SAS links out of its controller, this is usually used to allow for diverse electrical paths but can be used to connect a single disk to two controllers to better handle hardware failure. It's got nothing to do with SATA at all.

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  2. NL-SAS drives have the mechanical characteristics of 'enterprise' SATA drives, with SAS controllers - this is mostly in terms of reliability/endurance/error rates/etc. They're not electronically sata on the controller side of things, with a SAS bridge - they're SAS all the way.

    But, to answer your question specifically, no you cannot connect a NL-SAS disk to a SATA controller.

    To answer some of the other post here, many controllers will allow you to connect SATA disks to a SAS controller, but many raid cards will not let you mix SAS and SATA in a virtual disk pool - NL-SAS could, but at possibly a significant degradation in services.

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