Backplanes

[HCHTech]

I was poking around the intertubes yesterday, looking at server refurbs and ran into a question I'm sure someone here can answer.

I was looking at two similar 8-drive backplanes. One had two connections for RAID cables, and the other had four. Most of the RAID cards I've worked with have only 2 cable connections, each capable of connecting up to 4 drives. I think I've seen cards like this referred to as "8-port" referring to the maximum number of drives.

So....why would you use a 4-connection backplane that holds a maximum of 8 drives over a 2-connection backplane that holds a maximum of 8 drives?

Looking around, I found a picture of an Intel 4-connection backplane and the connections are labeled 1-Pri, 1-Sec, 2-Pri, 2-Sec. Which I guess is self-explanatory.

Maybe you want to run 4 separate RAID 1 arrays, each on a different RAID channel? Why would that be advantageous?

 

[coffee]

That and possibly thru put speeds?

 

[Alexey]

, I found a picture of an Intel 4-connection backplane and the connections are labeled 1-Pri, 1-Sec, 2-Pri, 2-Sec. Which I guess is self-explanatory

Dual RAID controllers?

 

[HCHTech]

That and possibly thru put speeds?

Yeah, I wonder how much that would matter. It would certainly be unusual (in my limited experience) to setup 4 RAID1 arrays on a server.

Dual RAID controllers?

Maybe, but to what end? The last RAID card I bought was about $700 (plus $200 for the flash backup) - that would certainly add a few bucks to the build using 2!

 

[Alexey]

Maybe, but to what end?

Redundancy with respect to controller failure. Really hard to tell as you do not list any model numbers.

 

[Markverhyden]

I can't remember ever seeing two RAID controllers in one server. Not even sure how that would work unless the firmware has the ability to communicate between the cards. That's in terms of failover/redundancy. You could certainly have two RAID controllers, each array would just show up as it's own config. But you can already do that with VHD's within a single RAID controller.

 

[Alexey]

Not sure about RAID controllers, but two HBAs in multipath configuration are certainly a reasonably regular practice. If one HBA, cable, or backplane port fails, the other picks up the throughput. Physical cabling is the same between RAID controller and non-RAID HBA.

 

[Markverhyden]

Not sure about RAID controllers, but two HBAs in multipath configuration are certainly a reasonably regular practice. If one HBA, cable, or backplane port fails, the other picks up the throughput. Physical cabling is the same between RAID controller and non-RAID HBA.

I've never done any configurations with newer HBA's, like fiber channel. Just an occasional break/fix on the box. The RAID cards in the typical server that I'd spec out for a customer is going to use SAS, or SATA if they are bottom dollar. In that respect the RAID card is a combination of HBA and RAID. The typical backplane I'd see in a server is just to interface the drives to the RAID card.

I have seen some higher level servers like an R930 that had both a RAID card, for internal dries, and a fiber channel HBA going to a storage array. But never had a chance to play around with them.