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I'm considering a QNAP 653D 6-bay NAS with 8GB of memory and an array of 12TB Seagate Ironwolf NAS HDDs configured in RAID 5 (initially with three drives that I bought on sale and expanding to 6 later). My environment has CAT 6 ethernet installed and I'm trying to figure out what speed switch and network adapter for my MacBook Pro to choose. While the QNAP NAS comes with two 2.5 GbE ports and can be upgraded to 10 GbE, I assume the HDDs are the bottleneck. My question is, what kind of speeds can I expect out of this NAS for read/write operations? Some articles online have suggested that the speed on the box of the HDDs is the maximum I can expect and therefore gigabit ethernet is sufficient. But in theory shouldn't the maximum speed be some multiple of that because the NAS has the ability to read data off of multiple disks in parallel as a result of striping? It's unclear to me what role striping and parity play in calculating what speeds to expect in read operations and write operations (i.e. slower/faster and by what magnitude).

For simplicity, let's ignore the fact that the outer part of an HDD drive is slower than the inner part as drives fill up and solve for the max speed scenario as I am just trying to ensure that the network is at parity or faster (i.e gigabit, 2.5 GbE, 5 GbE or 10 GbE).

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  • Striping isnt magical. You will be extremely lucky if you can come close to a 50% speed increase. 25% would be more realistic. Adding more drives will not help either, as there are drastically diminishing returns. There is only so much you can do with 7200 RPM spinning rust.
    – Keltari
    Commented Jan 22, 2021 at 3:08
  • Beware that raw "speed" numbers are often throughput maximums that are unencumbered with network protocol and filesystem overhead. The transfer speeds you will see in actual use will be less than these promoted numbers. Also consider the issue of concurrent requests/operations, which means that the network and/or storage are not dedicated to performing that one transfer you're timing.
    – sawdust
    Commented Jan 22, 2021 at 4:28
  • Why are you using RAID5? This is generally a bad idea - particularly on hdds
    – davidgo
    Commented Jan 22, 2021 at 6:51
  • @davidgo you're probably right. i should reconsider that and allow myself for more than one drive failure.
    – hughesdan
    Commented Jan 23, 2021 at 7:01

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It depends on how much you are willing to spend on the network infrastructure. CAT 6 ethernet can do 10 gigabit of data transfer. Consumer switches and what not are limited to 1 gigabit however. Anything faster would be enterprise grade. Finding even a 2.5 gigabit switch for less than $100 is not easy. The limiting factor here will actually be your ethernet switches, believe it or not. Good HDD can hit 200MB a second in sequential writes. This is much faster than the 120MB that a gigabit ethernet switch will get you. In random reads, your HDD might hit 50MB a second.

Using striping will increase the speed by up to 2x, since it can write to both drives simultaneously. This can increase with the number of drives that are striped, but it is not as simple as "4 drives= 4X speed." There are other factors. If you plan on having 4 or more drives in the NAS, even if one is used for parity, I would expect your network infrastructure to actually be the bottleneck on occasion.

If you plan to write large files above 120MB on a regular basis, say for video editing or a Plex server, then you may want to spend the extra on a 2.5 or 10 gigabit ethernet switch. They are 10X the price of a gigabit switch though, so you need to determine if it is worth it.

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