Raspberry PI / OMV... ethernet or wifi?

    • OMV 3.x
    • Raspberry PI / OMV... ethernet or wifi?

      I'd like to suggest to anyone running OMV on a raspberry pi for a home nas to use wifi instead of ethernet, as the wifi is on its own interface and therefore you should not have issues sharing bandwidth between the ethernet port and your storage.

      Just in case this was non-obvious, I noticed many tutorials online say to connect the RPi via ethernet and really this is a pretty poor idea if you're intending to r/w alot of data from anything other than the root partition.

      Cheers
      :cursing: Intel NUC Kit DE3815TYKHE My NAS build / ARK
      Atom E3815 1.46GHz4GB RAM • 1TB SSHD • 4GB eMMC
      OMV 3.x | OMV-Extras | Flash Memory | Pi-hole

      RPi/3 №1: LibreElec 8.xRPi/3 №2: SickRage, PiVPN, noip2
    • drinks2go wrote:

      I'd like to suggest to anyone running OMV on a raspberry pi for a home nas to use wifi instead of ethernet, as the wifi is on its own interface and therefore you should not have issues sharing bandwidth between the ethernet port and your storage.

      Just in case this was non-obvious, I noticed many tutorials online say to connect the RPi via ethernet and really this is a pretty poor idea if you're intending to r/w alot of data from anything other than the root partition.

      Cheers
      Thank you! I was just wondering if I should do this switch after reading that all USB ports AND the ethernet share a common bus.
      Is there a way to measure the transfer speed? I know on windows it shows it automatically if you're copying let's say a movie from your desktop to your NAS. But I'm using a Mac and would be really interested to see if transfer rate improves after switching to wifi...
    • drinks2go wrote:

      I'd like to suggest to anyone running OMV on a raspberry pi for a home nas to use wifi instead of ethernet, as the wifi is on its own interface and therefore you should not have issues sharing bandwidth between the ethernet port and your storage.
      Please do some research first. Using onboard Wi-Fi on Raspberries is a terrible idea since slow as hell.

      While it's true that Wi-Fi is 'on its own interface' this specific interface is even more crappy than the single USB2 connection those Raspberries suffer from.

      Wi-Fi on the RPi 3 and Zero is on SDIO (slow) and the implementation is just the definition of 'most crappy possible': it's 2.4 GHz band only (overcrowded as hell if you're living in any city), has only one antenna (for decent Wi-Fi performance you need MIMO and several antennas on both the client and the AP) and this antenna is crappy anyway (it's a miniature onboard thingy)

      Wi-Fi on those Raspberries provides under perfect conditions only 40% of the onboard Ethernet's 'performance'. In other words: those 4 MB/s while being on another bus do bottleneck even more than those 10 MB/s you get with the lousy Fast Ethernet implementation. If you want those most lousy devices for a NAS (RPi) then your only option to get a little bit decent performance is buying an external Gigabit Ethernet dongle (and even this is a terrible idea compared to replacing the RPi with something better) or a good 802.11ac/5GHz capable Wi-Fi dongle with 2 or even 4 antennas (for example RTL8812AU or RTL8814AU)
      • onboard crap Wi-Fi: 4 MB/s max (with 'perfect conditions' that do not exist especially in cities)
      • onboard 'Fast Ethernet': 11MB/s max (the slow '100 Mbps Ethernet' standard is the bottleneck not the 'shared USB bus')
      • external Gigabit Ethernet: 20MB/s (now USB2 and the 'shared USB bus' becomes the bottleneck)
      • external excellent Wi-Fi: up to 20MB/s (now USB2 and the 'shared USB bus' becomes the bottleneck)
      More details in case of interest: forum.armbian.com/topic/3739-w…-and-known-issues-on-sbc/

      The post was edited 1 time, last by tkaiser ().

    • Addendum: this is how capable Wi-Fi implementations for single board computers look like:
      [IMG:http://kaiser-edv.de/tmp/lGtv38/Size_Comparison.jpg]

      It's about dual band capabilities (2.4 GHz band is slow and especially overcrowded in every city in the meantime) and at least a dual antenna implementation (3 or even 4 would be better but you need at least same amount of antennas on the client and AP since otherwise it's of no use).

      To get performant Wi-Fi
      • you need 802.11n or 802.11ac implementing MIMO (2x2 or better),
      • you need real antennas and not this miniature onboard joke like on Raspberries and
      • you need to be able to make use of the 5GHz band to escape the slow and overcrowded 2.4GHz band.
      None of this you get with any Raspberry unless you waste roughly the same amount of money for an external Wi-Fi dongle as you had to purchase your RPi. An RTL8812AU based dongle as can be seen at the right in the above picture costs on average ~35 bucks, see here or there.

      The post was edited 2 times, last by tkaiser ().

    • hekmatk wrote:

      Is there a way to measure the transfer speed?
      Sure, on OMV there is either iperf3 pre-installed (on all the ARM images) or you need to do a

      Source Code

      1. apt install iperf3

      On Windows you then need jperf.exe (or something like that -- no Windows user here) while in macOS you simply install Homebrew if not already done and then it's a simple

      Source Code

      1. brew install iperf3
      Afterwards you start on one machine 'iperf3 -s' (server) and on the other one you use 'iperf3 -c' to test client/server performance or 'iperf3 -c -R' to test the reverse direction. Now to the performance numbers we get with synthetic benchmarks and then to the stuff this thread here originally tried to deal with: the crappy situation with 'shared bandwidth':
      1. iperf3 will report 40 Mbits/sec under best conditions (that do not exist in the wild) when you use onboard Wi-Fi. In reality and with some distance between RPi and AP this will be magnitudes lower (see real world numbers here)
      2. iperf3 will report +90 Mbits/sec when your RPi is connected via network cable (Ethernet is always at least twice as fast as onboard Wi-Fi)
      3. iperf3 might report ~350 Mbits/sec when you use a good external USB3 Gigabit Ethernet dongle connected to a GbE switch (now you're bottlenecked by SoC <--> USB2 <--> Ethernet dongle)


      How do these numbers translate to a NAS scenario where not only network is involved but also disk access?
      1. With onboard Wi-Fi always Wi-Fi is the bottleneck. RPi's implementation is 802.11n but only the slowest mode possible: 2.4GHz band and a single antenna so no MIMO (which is important to get any decent speed). You will not be able to exceed NAS transfer rates of 4 MB/s regardless what you do and usually it will be way less in crowded areas (Wi-Fi is a shared medium and all your neighbours flood the 2.4GHz band as well)
      2. With Fast Ethernet and appropriate settings (our OMV images are providing) you'll see now ~10 MB/s on average since USB2 is not yet the bottleneck even if every single bit transferred between client and server has to pass the USB2 bottleneck on Raspberries twice!
      3. With an external GbE dongle we're finally able to enjoy the 'shared bus' bottleneck since now the theoretical 'every single bit has to pass the USB2 bottleneck twice' comes into play. Due to disk access and GbE fighting for bandwidth the overall maximum transfer speeds are limited to below 20 MB/s


      To test for overall NAS bandwidth and latency issues I strongly recommend to always use 'HELIOS LanTest' (available for free). All these screenshots have been generated with it: forum.armbian.com/topic/3953-p…ges-for-sbc-with-armbian/

      If you really test with Wi-Fi on your RPi be prepared that in a crowded environment with tons of other wireless networks next to you you will see horribly low scores. Not only sequential transfer speeds (MB/s) but also affecting file handles (open, close, delete) which heavily affects performance of e.g. networked backup (TimeMachine for example)
    • Addendum: With the new RPi 3B + and its 802.11ac Wi-Fi implementation it's the first time possible to get somewhat decent wireless throughput numbers (bandwidth != latency) with a RPi that might even exceed those possible with an USB2 Wi-Fi dongle.

      Prerequisit: your RPi 3B+ must sit right next to an 5GHz capable access point. Only then you'll be able to benefit from bandwidths up to 230 Mbits/sec (6 times faster than with Pi 3 or Zero W). Some details: OpenMediaVault is incompatible with Raspberry PI 3B+?