I have a question about these SATA expansion / controller cards with regard to PCI-e slots and bandwidth. I notice that typically products will follow the below trend:
PCI-e x1 slot = 2 port expansion cards available
PCI-e x4 slot = 4 port expansion cards available (and some 8 port)
PCI-e x8 slot = 8 port + expansion cards available
I understand that this is to do with bandwidth of each slot and not producing products that would be bottlenecked by each slot. However, the above does not make sense to me…
Why do we not have for example 4 port cards available for PCI-e x1 slots? PCI-e version 2.0 x1 slots, have a maximum bandwidth of 500 MB/s. Taking the assumption that each drive attached to this slot could be reading/writing at a theoretical 125MB/s each (max possible over gigabit ethernet) then we have:
500 / 125 = 4 possible drives
So we could have 4 hard disk drives attached to a PCI-e 2.0 x1 slot if they manufactured a card that had 4 ports. Yet we only see cards with 2 ports on x1 slots.
I can understand this scenario if you take into account the cards are only manufactured for PCI-e version 1.0/1.1, as then the bandwidth is halved to 250MB/s, so the above example would check out and you could have exactly 2 HDDs attached before theoretically hitting a bottleneck. Is this all it is? That nobody has bothered making a PCI-e version 2.0 x1, 4 port card? Can I assume that the reason is due to lack of demand when people can use the already out there products for x4 slots?
Reason I am interested, is that my motherboard has 2 separate x1 slots (PCI-e version 2.0) and I am trying to plan for the future what the maximum amount of hard disk drives I could handle is. I have on my motherboard:
8 x SATA ports
1 x 16x pci-e slot (version 2.0)
2 x 1x pci-e slot (version 2.0)
I think I can have 8 + 8 + 2 + 2 = 20 which nicely maximises the current licence for Pro I believe.