SMB2 - Suddenly only small block sizes requested by client

asked 2019-09-30 14:01:09 +0000

wshark_de gravatar image

updated 2019-10-01 08:12:12 +0000

Dear lovely community, one of our clients has problems with his file transfers (from 50Mbit/s to 0,7Mbit/s), which suffer from suddenly decreasing block read sizes (from more than 1MB to 4kb) beginning in the middle of TCP stream graph. Only about 4 TCP errors before, nothing special here. Any idea why this happens? Stream Graph and Packets

Can somebody read those SMB credit graphs, because maybe its related to them? Seems like client stops requesting credits, but why would a client do so? SMB Credits Windows 10 Client, Server 2016 in Azure Cloud.

Thank you!

edit retag flag offensive close merge delete


it seems your receiver windows is reached around ~7965969 B, after a period of waiting, then sligthy increase the capacity and then waiting period again, in can be also anything in the middle. Let's assume it either the sender or the receiver, .... Could you print the commands from Get-Smblclientconfiguration , or Get-SmbServerConfiguration from the powershell command on windows systems. Also take a look to the Microsoft SMB tunning page SMB performance

xinxolHH gravatar imagexinxolHH ( 2019-10-01 08:04:23 +0000 )edit

Thanks, I will have a look at those outputs.

wshark_de gravatar imagewshark_de ( 2019-10-01 09:21:28 +0000 )edit

We found a scheme when this happens. It happens for SMB database transfers only, after double-clicking the database file Microsoft Access opens and a lock file ".laccdb" is created. After this file is created, only 4KB block sizes are red. It is a reproduceable scheme. But as a network engineer, I dont know why it behaves this way, yet.

wshark_de gravatar imagewshark_de ( 2019-10-02 10:06:59 +0000 )edit

thanks for the update. I only think now in potentally row lock mechanism on the Access database when inserting process.

xinxolHH gravatar imagexinxolHH ( 2019-10-02 11:41:42 +0000 )edit