Where is my SMB file transfer bottlenecking at?

[ShimadaRiku]

ESXI 6.5
32GB ECC ram
Intel 1231v3

Virtualized FreeNAS 11.2-U5
LSI 2308 passthrough
6x8TB Raidz2, 1M recordsize, sync=disabled, 24% full, 12% frag
VMX3NET virtual nic

Virtualized Win10
SSD OS datastore
VMX3NET virtual nic

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In Win10 desktop environment I copied large files from SSD to FreeNAS share via the explorer. When I was using FreeNAS 9.3 it didn't support VM3NET virtual nic so the E1000 capped out at ~150 MB/s. Upgraded FreeNAS to 11.2-U5 and file transfer now caps at 300 MB/s

My 8TB drives are WD white shucked from easystores enclosures. Write speed should be on avg 120 MB/s per drive so a 6x8TB should in theory reach 480 MB/s+ but I'm capped at 300 MB/s

Further testing I tried using diskspd.exe MSFT utility to benchmark SMB transfer

Code:

diskspd.exe -c2G -b1024K -t1 -d10 -L -o1 -w100 -D -h E:\testfile.dat

Write speed result from the benchmark was 439 MB/s so it can achieve faster rates. So why is my windows explorer file transfer capped at 300 MB/s. Is it a setting or something bottlenecking?

 

[seanm]

Have you compared speed of a single large file vs many smaller files?

 

[ShimadaRiku]

Have you compared speed of a single large file vs many smaller files?

I transferred a dozen or so 2-3GB files.

Small files like documents etc would be even lower throughput.