Bizarrely horrific SMB speed on Windows (vs WSL+CIFS)

TrueNAS General
1

So suddenly my Windows SMB speed plummeted. Like from GB speeds to < KB speeds.

I COULD have happened after an upgrade to the new 24.10 beta. Timing is about right.

But what is weird is that a CIFS mount in WSL running on the EXACT SAME windows machine performs normally while the native Windows (11…latest stable) share has performance issues. Also if you use the drvfs mount instead of cifs, you see the horrid native Windows performance (understandable since drvfs is just a translation layer on top of the windows file system).

For example, a directory with 5157 files totaling 53,546,183 bytes takes a few seconds to transfer under WSL, but likely over an HOUR using the regular windows share.

Same performance issue for all SMB shares hitting this TNS box.

What could possibly be causing this? Obviously not a network issue. Not a ZFS issue. Gotta be something in the SMB config on Windows from an update or maybe something that’s new with 24.10. Where do I start?

2

I can tell you I saturate Gigabit lan with Eel as a VM under Dragonfish, so, I doubt it’s Eel!

3

I’ve had a couple of read/write performance issues before. They may not match your issue, but may be helpful.

  1. My SMB transfer speeds dropped ~85%. I fixed this by pushing my LAN cable further into my PC. Apparently, there is a tiny amount of slack in the connection and when it isn’t fully seated, the connection drops from Gigabit to 100 megabit, which I happened to notice in my switch’s UI.
  2. Every once in a while, I encounter this strange issue with rsync where speeds will drop from ~80 MB/s down to sub-KB/s. I have no clue what causes this, but it drives me crazy. Fortunately, I do not see this that often and am not sure what fixes it.
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Thanks for the replies. I further narrowed it down to just that one Windows PC. No issues at all with a different PC.

So I tried a different cable from PC to switch. No difference. So I got a LONG cable and ran it from my PC to my central switch. That made a huge difference, despite a speed step down from 2.5 to 1Gbe.

So I’m COMPLETELY baffled now. Again, the SAME PC running CIFS virtualized using Windows Subsystem for Linux runs just fine. But just switching tabs in my terminal and running using native Windows SMB to the same exact share copying the same exact files and it’s complete crap. But ONLY through my remote switch.

iPerf3 is basically showing full 2.5Gbe from this Windows client to the TNS server through the switch, so it’s not a bandwidth thing. There must be some kind of packet size, buffer overflow shenanigans going on with the switch that’s just fundamentally incompatible with my (admittedly sketch) Vimin 10G/2.5G switch.

Short of buying a new switch and chasing rabbits is there anything in this explanation that says “ah ha, I think I have an idea” to anyone?

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