Max throughput on the PCIe 2 and 3 bus

[tived]

Hi guys,

What is the max throughput one can expect on PCIe 2 and 3?

In my case in point it will be using an Areca 1882ix 24 and two IBM M1015's

at the moment i have 12 Intel 520 120GB, but only 8 in raid as i use the 4 others as boot, but will reorganize them shortly to test

Trying to work out how many drives I need to just sit below it?

Thanks for taking the time

Henrik

[johnw]

Each lane of PCIe is bidirectional (i.e., you can read and write at the same time without either affecting the other), but I will quote the specifications for a single direction.

PCIe 2.0: 5 GHz with 8b/10b encoding gives 500 MB/s per lane per direction

PCIe 3.0: 8 GHz with 128b/130b encoding gives 985 MB/s per lane per direction

That is the theoretical maximum that each PCIe standard can support. In practice, you will not reach that speed. As a rule of thumb, use 80% of that speed as an estimate of the maximum practical throughput.

M1015s have 8 lanes of PCIe 2.0, so that is 4000 MB/s max theoretical max, but figure on 80% of that, so 3200 MB/s or less in practice.

[tived]

Thanks John,

So if can get close to 3 Gb/s that would be good - though I doubt that will happen on the M1015, I have not been getting very good results on that, with my 8x Intel 520 drives. The Areca is performing better, but was also 10x the price, though not 10x faster :-)