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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.

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Based on your comment to Chopper3, it sounds like you really want reliable SATA disks. Both Seagate and Western Digital have "Enterprise SATA" models, that feature some more advanced features; better reliability specifications; higher duty cycles; and larger capacities than regular desktop drives. Look for Seagate Constellation ES or Western Digital Raid Edition (RE) drives. –  Daniel Lawson Jun 20 '11 at 10:26
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2 Answers

up vote 7 down vote accepted

"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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Note that I have 0 experience in SAS. I'm looking at ordering a budget server (really for home purposes) and wondering what level of enterpriseyness (is that a word?) I can incorporate taking into account that I may need to attach the drives to a consumer machine at a later date. But thank you for your info. –  Vincent Vancalbergh Jun 20 '11 at 10:23
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If you want 'enterprise' features go for a Xeon E3 or 56xx-series CPU, use their triple-memory-channel capability, team your NICs and get a machine that has the capacity for dual power supplies. It's the resilience and linearity of performance fall-off that differentiates a server, not just the outright unloaded 'power'. I love SAS/FC/FCoE and it's while it's important to have multiple controllers and paths on a server performance is secondary to stability. –  Chopper3 Jun 20 '11 at 10:40
    
This isn't a production server that needs 99.9% uptime. If I'm out of business for 2 or 3 days it's no biggy. For me performance matters and good, frequent backups. I agree, when my business gets beyond "mudding about after hours", stability will pop up headfirst (like it does at my clients). Good advice as well :) –  Vincent Vancalbergh Jun 20 '11 at 11:19
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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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Thanks, the explanation of what NL-SAS internally is was how I preceived it to be. You just worded it best of all :). –  Vincent Vancalbergh Jan 8 '13 at 20:06
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