[Samba] Performance Degradation when copying >1500 files to mac

[Christian Kuntz]

Hello all,

I'm running into a significant performance issue where copying a couple
thousand <3kb files from my stretch SMB server to a mac client. Dragging +
dropping the files from the gui results in a long period of time in which
the client is "preparing to copy" and then actually transferring, during
this time transfer starts around 300MB/s, then after around 5-10 seconds
drops to <50MB/s and eventually recovers after a few minutes. The more
files being copied, the more pronounced the drop off is and the slower the
bandwidth. If two clients are doing the copy at the same time, they'll both
slow eachother down significantly, even if it's done manually via cp on the
command line.

The server is running debian stretch, SMB 4.5, backed by ZFS 0.7.13. The
mac os client is running Darwin 18.7.0 (have also tested and confirmed
behavior on Mojave 10.14.6) and writing to SSD, and I confirmed that
comparable FS operations locally do not incur the performance penalty, only
from SMB to disk.

iperf gives the connection speed its full line rate of 10gbps, and disk
read performance of the smb server is >10gbps.

I've tested the same operations from linux <-> linux via the smb share, but
no performance drop off was seen. Further, copying large files back and
forth also saw no problem.

I'm wondering if anyone might have any knowledge as to particular smb
client configuration settings on the mac side that may help alleviate this
issue, or if this is a known problem with current mac smb clients?

Thanks for your time

Best regards,
Christian

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