How many parallel drives, configured with RAID 0 striping (nX sequential read/write benefit) and sitting behind a hardware RAID controller (PCI-X at 133MHz) does it take to saturate a 1Gbps network connection? What about 2Gbps?
When setting up a small NAS, a big variable is the network connection. One can go with a single gigabit ethernet connection, bond several together (with managed network switches), or go with more expensive fiber channel options. Sticking to CAT5e/6 cables reduces costs to what I can manage, but I still want to get the most out of it without introducing wasteful bottlenecks.
Referring to Seagate's example of an external transfer rate (burst) of around 300MB/s (2.3Gbps) and one of storagereview.com's 3TB reviews showing sustained transfer rates of around 110MB/s (0.9Gbps), I have to come to the conclusion that there is no noticeable performance benefit to setting up RAID striping among multiple parallel drives when accessed through a 1Gbps line. A single drive uses nearly 1Gbps of bandwidth.
Of course, the data has to jump a few hoops to get from the drive controller to the cable, reducing the effective server transfer rate. Even more overhead is introduced by a RAID controller, though the parallel drives more than make up for it, but by what margin? Hence my question.
Note that a 133MHz PCI-X connector can support up to 8.5Gbps [Wikipedia]. Try to ignore the differences between stripe sizes, protocol overhead, etc., and look at the issue from a hardware perspective alone.
My NAS motherboard 'A' (with 'B' GB of RAM) and [133MHz PCI-X] RAID controller card 'C' have a maximum throughput of about 7Gbps. The limiting factor is the ethernet controller. I have observed that a 1Gbps/2Gbps connection becomes saturated with as few as 2 drives/3 drives, at around 100MBps/200MBps using iperf.