Port multiplier vs. second HBA?

[Carson Dyle]

I have a server with an LSI 9211-8i running in IT mode. The system also has Supermicro PCI-X controller with an additional eight hard drives. I'm thinking of moving to a new motherboard and CPU, and would lose the PCI-X slot, so to support a similar number of drives I'd either get a second 9211-8i or else I can add a port multiplier.

I've never worked with a port multiplier. Would there be any significant loss in performance vs. using a second 9211-8i controller? Are there any other factors to take into consideration, performance-wise?

 

[XavierMace]

Depends what you have plugged into the controller. Each plug on your controller has 4 lanes rated for 600MB/s per lane. If you're running plain 7200rpm spindles, you aren't going to saturate that with 4 drives per plug, so adding an expander isn't really going to negatively impact your performance. If you're running all SSD's though, you're probably already saturating the controller, so using an expander to add more drives is going to degrade max throughput.

 

[dave_the_nerd]

Looks like those cards are around $70 on ebay. A port multiplier is usually ~$30, so that's the downside.

IME multipliers can sometimes be a little flaky. $40 is worth better reliability, IMHO.

But it's your money.

 

[XavierMace]

I'd agree, unless you've got a case with a built in expander/multiplier. I went from a Norco case with just a pass through backplane to a Supermicro with an expander backplane. So, yeah, I loss some throughput capacity, but now I only need one card and cable for my drives so it was worth the trade off to me.

 

[Carson Dyle]

It's all 5400 RPM hard drives. The other consideration is a need for the replacement motherboard to have two PCIe x8 slots if I add a second 9211-8i.

 

[XavierMace]

If it's all 5400rpm drives, performance isn't really a concern so I'd probably just go the cheapest option.

 

[dave_the_nerd]

It's all 5400 RPM hard drives. The other consideration is a need for the replacement motherboard to have two PCIe x8 slots if I add a second 9211-8i.

Well, if you're replacing the motherboard and CPU anyway, that shouldn't be especially difficult to find.

 

[Carson Dyle]

Well, if you're replacing the motherboard and CPU anyway, that shouldn't be especially difficult to find.

The point was that it places an additional requirement on the board, one that is likely to cost more. It eliminates quite a few inexpensive mini-ITX boards.

 

[PingSpike]

Are there any special considerations with port multipliers? Like SATA version support, controller support, etc? I've never used them before but it seems like it might be a good way to get a lot of drives in a NAS based on those low power boards that usually have a crappy about of SATA ports.

 

[master_shake_]

i've never had an issue with using expanders on sata drives.

my experience includes, 2 intel 24 port expanders, 36 port hp sas expander and a 16 port ibm expander.

all used with lsi sas controllers that are an ibm 5015 (lsi 9260-8i), lsi 9260-4i and an lsi 8888elp.

 

[daxzy]

Just stumbled onto here...

I built my storage system in early 2014. SAS 6G expanders were much more expensive then. I checked eBay and saw an Intel 24 port SAS expander was only $140 (RES2SV240NC). Do these work with a HW raid card in IR (not IT) mode (e.g. LSI 9261-8i)?

 

[master_shake_]

Yes they do.

The card is invisible to Windows and works flawlessly with LSI cards because it is an Intel branded lsi expander.