How do I connect so many drives to a single RAID controller?

Question

Please excuse my noobishness; I am trying to get up to speed with current technology.

When looking at this 3ware RAID controller, I see that there is only one plug, yet the controller says it supports up to 127 devices. Assuming I actually wanted to attach 127 drives to this controller, what would I need? I assume I would need a Mini-SAS cable which fans out to 4 SATA plugs, and then I would need to use 4 massive SATA port multipliers. Is that correct? It sounds like a huge opportunity for a bottleneck if all 127 drives are ultimately connected by 1 port.

There are a couple more interesting specs listed for this drive: it says "Up to 32 active units support" and "Up to 32 drives per unit support". What does that mean? Surely the specs aren't being contradictory, saying that up to 32 x 32 drives are supported.

I would appreciate any pointers to resources that can get me up to date with the current technology. I am familiar enough with RAID technology to be able to build and maintain a small one (< 16 drives), but I am curious about how the pros go about building massive storage machines.

Answer 1

Yes, you need SAS expanders to get all the drives on there. Look up Backblaze's storage pods : http://blog.backblaze.com/2009/09/01/petabytes-on-a-budget-how-to-build-cheap-cloud-storage/

That card says it's a 4-lane port, so that's somewhat of a bottleneck. They make cards with more ports.

Answer 2

It appears that the largest card supports 28 drives at this time, however there may be a way of connecting that to special backplanes may provide extended drive splitting up to the 32 drives/units.

http://www.lsi.com/downloads/Public/RAID%20Controllers/RAID%20Controllers%20Common%20Files/InstallGuide9750_10.2codeset.pdf