1 Replies - 388 Views - Last Post: 18 August 2019 - 06:28 PM

#1 victorman   User is offline

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Help me find the data rate bottlenecks

Posted 18 August 2019 - 05:01 PM

I recently made a Raspberry pi 4 NAS. I knew the performance wasn't going to be the best, but for the price of a the pi kit (and a case) I can plug my externals into it and serve up a SMB share pointing to my externals in some corner of the room, and I don't have to dig them out and clutter my desk whenever I want to watch something in my movie collection. I'm happy.

But for my own edification I want to calculate the effective speeds I'm getting from this device. And should I add drives later how to get the best speeds possible.


Looking at the data path I guessed the greatest bottleneck to data transfer rate would be the USB 2.0 from external drive to pi at USB 2 speeds of 60MB/s resulting in a rate slightly less. But I'm finding it's half that at about 32 MB/s. I want to make sure if I add extra drives onto the usb 3 ports i'll actually see improved speeds but if that's not the case i might as well save my money.

  • External HDD (assumed USB 2.0) - 60 MB/s
  • Raspberry Pi 4 B, 4GB RAM, running raspbian lite Buster, with openmediavault with Gigabit ethernet connection - 1024 MB/s
  • Gigabit ehternet switch Netgear GS208
    >
  • Netgear Nighthawk R6700 802.11ac - numbers range from 433 MB/s
  • Laptop wifi NIC is 802.11ac ostensibly
    -
  • ALTERNATIVE Laptop Gigabit ethernet - similar outcome to wifi
    >
  • Laptop ssd samsung 820 EVO


Bitlocker is enabled, i do have browser open to various websites. I will try again without.

I'll gladly post as much information as you guys want. Help me figure this out.

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Replies To: Help me find the data rate bottlenecks

#2 victorman   User is offline

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Re: Help me find the data rate bottlenecks

Posted 18 August 2019 - 06:28 PM

Well here it is. I found the disk is actually 31.5 MB/s not the 60 MB/s I assumed.

running the following on the raspberry pi
$ hdparm -t /dev/sda1

/dev/sda1:
Timing buffered disk reads: 96 MB in 3.05 seconds = 31.51 MB/sec

This post has been edited by victorman: 18 August 2019 - 06:29 PM

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