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Help with understanding throughput of pcie and hard drives (lemmy.world)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

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I've been interested in building a DIY NAS out of an SBC for a while now. Not as my main NAS but as a backup I can store offsite at a friend or relative's house. I know any old x86 box will probably do better, this project is just for the fun of it.

The Orange Pi 5 looks pretty decent with its RK3588 chip and M.2 PCIe 3.0 x4 connector. I've seen some adapters that can turn that M.2 slot into a few SATA ports or even a full x16 slot which might let me use an HBA.

Anyway, my question is, assuming the CPU isn't a bottle neck, how do I figure out what kind of throughput this setup could theoretically give me?

After a few google searches:

PCIe Gen 3 x4 should give me 4 GB/s throughput
that M.2 to SATA adapter claims 6 ~~GB/s~~ Gb/s throughput
a single 7200rpm hard drive should give about 80-160MB/s throughput

My guess is that ultimately, I'm limited by that 4GB/s throughput on the PCIe Gen 3 x4 slot but since I'm using hard drives, I'd never get close to saturating that bandwidth. Even if I was using 4 hard drives in a RAID 0 config (which I wouldn't do), I still wouldn't come close. Am I understanding that correctly; is it really that simple?

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[–] [email protected] 3 points 1 year ago (1 children)

I wouldn't be surprised if you could find something with more ports available if needed, or at least for a cheaper price.

Based on another comment I read, each SATA port would be 6 gigabits/s which equates to 0.75 gigabytes/s. If I fully saturated all 5 ports, that puts the throughput at 3.75 gigabytes/s. Anything over 5 ports would be bottlenecked by the M.2 PCIe Gen 3 x4 port wouldn’t it?

[–] [email protected] 2 points 1 year ago (1 children)

Yeah but you're not going to saturate each SATA port with your harddrives, which will be closer to 2 gbps max. The PCIE connector only needs to worry about what actually goes across it. I imagine that card is built to spec with the situation you're describing in mind, but for more practical purposes I think it shouldn't be a problem to have even more slots?

[–] [email protected] 1 points 1 year ago

Oh that’s right, I didn’t take into account the speed of the hard drives. Sweet