RAID card w/1x mini-SAS connector : how do I physically connect 16 disks?

Question

I'm looking at a MegaRAID SAS 9240-4i Sgl card which has a single X4 Mini-SAS SFF8087 connector. As far as I know, such a connector can be expanded to 4 SATA disks. So, I would know how to connect 4 SATA disks. However, the documentation says it supports up to 16 disks in a RAID volume. My question is then; how do I physically connect these 16 disks to the card which only has a single connector?

Is this where backplanes come in (I've tried to find information on that, but can't really figure out how they work together with the RAID controller). ?

Solution 1

Yes, this is where SAS expanders, enclosure backplanes and breakout cables come in. You can obtain a breakout cable that will provide 4 ports from the SFF-8087 mini-SAS connector. You can also try to use something like the HP SAS Expander to provide more SFF-8087 ports for your use from the single RAID controller. A detailed forum about the HP expander is available here.

I mentioned backplanes only because some have embedded expanders that allow them to accommodate more than 4 or 8 drives. You're probably not working with a system with a SAS backplane, so disregard that part and focus on expansion at the RAID card level.

Solution 2

1. Stay away from the MegaCrap cards. LSI bought them for who-know-what-reason and should have put them out of their misery long ago. Get one of LSI's own SAS HBAs (assuming you want something good and from LSI, other manufacturers are out there too).

2. There are "SFF-8087 to 4x SATA" cables around to plug such cards into 4 SATA drives. You can find them on eBay for $5.

3. It's a SAS HBA at it's heart. So you can use a SAS Expander board (or backplane) to attach more SATA drives to that one HBA. The SAS Expanders simply have 1 "upstream" port and multiple "downstream" ports, pretty simple stuff.

Comments

[ewwhite]

What type of RAID card are you using? Make/model.

[sbrattla]

Does the SAS HBAs provide RAID? I'd like to use a MegaRaid card as I've already got two Dell servers with PERC controllers (rebranded MegaRaid) and I thus can use the same monitoring software.

[TomTom]

@srattle A SAS HBA is a HBA. Point. It CAN provide RAID, then it is a RAID card. It depends on the product features. THAT SAID: ther are some good reasoons against using raid cards depending what you do (ZFS for example prefers software raid and is VERY powerfull). But generally, HBA are not raid cards - Raid cards are more expensive. It always depends though - so reading is a must.

[sbrattla]

Alright. So I could go with the RAID card which provides a single SFF-8087 connector and connect that to a SAS Expander card which would turn that single port into more SSF-8087 ports...which each can manage 4 SATA disks?

[Philip]

If you've got the PERC cards already, you'll probably just want to stick with that model for consistency sake. The LSI HBAs support R0, R1, and R10 out of the box; some can be "upgraded" to support other modes.

[sbrattla]

@Chris The rebranded MegaRaid (as PERC) has worked well in the Dell machines I'm running. However, the PERC cards are rather expensive to buy from Dell so I was looking at getting a LSI card instead.

[sbrattla]

Say I do that (RAID card -> expander card -> 16 disks) and a disk fails. I would then check the monitoring software for the RAID to see which disk I would have to physically remove. Is it somehow fairly common for the RAID cards to be able to use the led's on the bay to identify the failed disk?

[ewwhite]

I don't know what type of server, enclosure, controller or disks you're using. I can't answer that without the right info.

[sbrattla]

Sorry for not posting that initially, just thought it would be a bit too specific. But the enclosure would most likely be norcotek.com/item_detail.php?categoryid=1&modelno=RPC-3216 and the controller would be the MegaRaid 9240-4i with a SAS expander such as the one you've mentioned.

[ewwhite]

Okay. That would work. Drive LEDs depend on the carriers, but they should work. I'd personally go with a controller that could support all of the requisite ports, but the expander works, too.

[sbrattla]

@Chris S I'm looking at the HP Expander and the documentation says "Cache availability—A cache module must be installed on the Smart Array P410 or P410i Controller.". I assume that is optional, and that as long as I've got the RAID controller "fronting" the SAS expander I will be able to use the cache functionality as provided by the RAID card?

[ewwhite]

@sbrattla That's a reference to the HP RAID controllers that the expander is meant to be used with. It's irrelevant in your case.

[sbrattla]

Marking this answer as correct. It answered the question very well, and I really appreciate that ewwhite has taken the time to answer my additional comments/questions as well.

[sbrattla]

Thanks for your answer Chris S. I've upvoted your answer.