Am I reading this right?

[Kelvarr]

I am in the process of building a storage array, using a Supermicro 846 chassis. Now...I don't know if I ever really intend to fully fill this beast of a case, but it was free to me, so I'm utilizing it. My last piece(s) I need are HBA's.

I did some quick napkin math, and wanted to see if I am interpreting my numbers right. I ran these numbers with a 30% overhead over theoretical.

Even if I ran all SAS3 drives, a PCIe 3.0 8x slot has enough bandwidth (6200 MiB/s) to handle 25 SAS3 drives (240 MiB/s)...am I correct in that?
In other words, a 24i HBA in a single PCIe slot or a 4i HBA with a 28i Expander (occupying a totaly of 2 slots) would completely cover this 24 bay case.

 

[ano]

you get somewhere in that land from the controllers, like 3008 yes, iirc its like 6400MBs

 

[Moopere]

I've gone down this rabbit hole in the past I found it more condusive to real-world expectations if I concentrate on IOPS rather than interface speeds

Plugging some numbers into my rough-n-ready spreadsheet:

25x SAS 15K 12G drives (using specs from : Seagate 2.5" 15E900)
RAID0
IO Block size 1536

Is likely to achieve real-world performance thats probably going to be verifiable to within a reasonable margin with a tool like Crystal Disk Mark:

214MB/s per drive
53 Gbps for the stack

Assuming no bottlenecks between the pci slot and the drives. Which RAID card you use and whether you use an expander will have an effect on things, so best to check the specs of your equipment and downrate based upon spec.


Alternative numbers:
25x SATA 5900RPM 6G (using spec from Seagate Ironwolf 3TB)
RAID0
IO Block size 1536

108MB/s per drive
27Gbps for the stack.

RAID 5 with the SATA drives above:

Assuming 20%W/80%R

About 91MB/s per drive
23Gbps for the stack.