SFF/LFF expander vs extra controller - what are pros/cons of each?

[6BQ5]

Adding additional 8-bay SFF or 6-bay LFF cages requires either an expander kit or a separate Smart Array Controller. The expander kit allows daisy chaining additional cage to the on-board controller whereas a separate Smart Array Controller installs into an available PCIe slot.

I'd like to know the pros and cons of each option. Would I get better read/write performance with an additional controller for each cage? If yes then would the ultimate setup be a Smart Controller card for each cage? Or, is there no performance benefit to separate controllers?

The expander kit part numbers are 661717-B21 for LFF drives and 661714-B21 for SFF drives.

Thanks!

[Torsten.]

Using the SAS expander creates fan-out connections, no daisy chain.

So the controller can use more physical drives, you can extend your arrays across more disks.

The controllers can handle a lot of disks, so there is no potential performance hit.

Using separate controllers limits the size of the arrays to a single disk box.

[6BQ5]

Hi Torsten,

Thanks for the reply!

It sounds like a controller is better suited when adding external storage appliances. I don't have any plans to add external storage appliances. The internal drives should give me enough space.

My ML350p Gen8 currently has a Smart Array 420i controller with a 512 MB FBWC controller. I believe the internal controller offers 6 Gb/s transfer speeds. The P430 and P830 cards offer 12 Gb/s transfer speeds. Do you this extra speed capability will be used with mechanical magnetic drives?

Or, do you think I would be better served getting one of the expander cage kits and increasing my FBWC from 512 MB to 2 GB or even 4 GB?

My end goal is to have two cages (probably staying with 8-bay SFF) plus one media bay kit (p/n 661618-B21). What do you think?

Thanks again!

[Torsten.]

Even if you have 12Gbit disks and controllers, the backplane in this servers limits to 6Gbit.

[6BQ5]

Replying to my own thread here ...

I just took a look at the prices of the various expansion options.

An 8-bay SFF expander cage kit is wickedly expensive!

It is much much much cheaper to get a stand-alone cage and an external controller. How much trouble would I get into if I do that?

Thanks!