2nd HBA vs SAS Expander

[SaberSHO]

I need a bit of advice on how best to configure a storage server based on Tiered Storage Spaces. I have an IBM x3620 M3 with the following (the case was modded to fit the SSDs):
6x 1TB SATA drives (7200)
2x 4TB SATA drives
4x 240GB Intel SSDs
1x SSD Boot drive

The spinning drives are currently connected to a M5014 via the server's drive backpane, each in fake passthrough, basically single drive raid 0 arrays x6. The SSDs are connected via a Dell H200 flashed to IT mode and a SAS->4x SATA breakout cable. I know that the fake passthrough on my spinning drives is a problem, and I would like to get them connected using an HBA.
My question then becomes if there is any pros/cons to using a SAS Expander vs just putting in a second H200 flashed to IT mode. The server has 3 PCIe slots (x16, x8 and x4), 2 of which are currently populated by the M5014 and the H200. The third will be a 10GB Mellanox card once it arrives. I thought I had read mentions that a SAS Expander may downgrade all sata traffic to SATA 2 (3gbps) speeds, and I would like to keep everything at 6gbps.

Thanks for any suggestions, and please let me know if anything is not clear.

 

[Aestr]

An expander will only lower your speeds to 3gbps if you get one that's capped at that speed. Most of the current popular options are 6gbps so over a single SFF-8087 cable you'll be sharing 24gbps back to an HBA.

I'd go with HBAs if you're not planning to go past 2 HBAs worth of drives in the long run. Your drives will be directly connected with each one getting it's own 6gbps pipe and you provide the most simple interface, limiting potential issues. It's usually a touch cheaper too. For spinning disk you likely won't be limiting your speed, but as you start adding more SSDs an expander will limit you.

Reasons to go with an expander:

- You plan to have more than 2 HBAs worth of drives, at which point it's often cheaper and uses fewer PCI-e slots
- You want a chassis with an expander backplane. This can really clean up cabling in larger systems
- You have limited pci-e slots (some expanders don't need a pci-e slot for power)

I hope that helps. If you have more questions let us know.