this post was submitted on 25 Sep 2023
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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 a_fancy_kiwi@lemmy.world to c/selfhosted@lemmy.world
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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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[–] Shdwdrgn@mander.xyz 4 points 1 year ago

Just for some real-world comparison, I set up a new NAS earlier this year using a rackserver, SAS cards, and eight 18TB HDDs configured like RAID6 (actually using zfs-z2). I played with a few different configurations but ultimately my write speeds reached around 480MB/s because of the parallel access to so many drives. Single drive access was of course quite a bit slower. Because of this testing I knew I could use cheap SATA2 backplanes without affecting the performance.

So basically, do a lot of testing with your planned hardware to get the best throughput, but a single HDD is going to be your single biggest bottleneck in anything you set up.