Fast then slow SMB transfers

[Bitbass]

I've been reading about some options for fixing this, but I'm not clear on what is safe to try.  I'm running 6.6.6 and mainly doing SMB transfers from a Windows 10 PC.  I've enabled jumbo frames on the switch and also set Unraid to an MTU of 9000.  Confirmed 1GE network through the whole path.  I have not messed with Turbo Write yet, so the tunable is still set to auto.  240GB SATA3 SSD for cache.

 

When I write from my Win10 PC HDD to an Unraid SMB user share using the cache disk it starts at 100MBps+ and somewhere around 2GB of transfer it slows to almost nothing before creeping back up to about 15MBps.  This is fairly consistent, although the 2GB limit is not a hard limit as far as I can tell.  It's only around that size where it slows dramatically.

 

Should I set the tunable to "reconstruct write"?  Is there something else I need to be looking at?

[Squid]

20 minutes ago, Bitbass said:

Should I set the tunable to "reconstruct write"?

 

21 minutes ago, Bitbass said:

to an Unraid SMB user share using the cache disk

Won't make a difference

 

21 minutes ago, Bitbass said:

Is there something else I need to be looking at?

Diagnostics might help

[Saldash]

I'm going to comment to follow this one as I've seen very similar behavior in my own file transfers, again, over a Gigabit ethernet on a run of only 10 feet.
Although I think I've read somewhere that RAM / spare RAM on the receiving end having something to do with it.

[JorgeB]

It's normal to get line speed for a few GB while transfer fits in the RAM cache, by default 20% of free RAM, after that you get the actual device speed, though 15MB/s is too slow, but it rules out network problems.

[Bitbass]

I have 16GB of RAM with only 12% in use at the moment.  Just had another problem with my SSD cache drive misbehaving.  I'll get that resolved and then run some more tests and post the diags if it's still an issue.