This is because the SMB request is first translated to a file system command and then to the actual file system latency to complete the operation. Or some variation of the create command creates the actual file.Įach create command generates activity on the file system.Īfter the data is written, the file is closed.Īll some time, the process suffers from network latency and SMB server latency. Some code will check whether the file exists, and then create the file. SMB calls a create command to request that the file be created. The following are technical details about this problem: When a large number of small files are transferred, the cost is repetitive and causes slow transfers. For large file transfers, these costs occur only one time. This is an expected behavior.ĭuring file transfer, file creation causes both high protocol overhead and high file system overhead. Slow transfer of small files through SMB occurs most commonly if there are many files. To do this, run the following command: Set-SmbClientConfiguration -EnableBandwidthThrottling 0 -EnableLargeMtu 1 On the SMB client, enable large MTU in SMB, and disable bandwidth throttling. This can cause throttling by the TCP congestion provider.įor SMBv3 and later versions, make sure that SMB Multichannel is enabled and working.
Use RAMMap (SysInternals) to determine whether "Mapped File" usage in memory stops growing because of free memory exhaustion. For more information, see Performance tuning for SMB file servers. Use storage performance monitor counters to determine whether storage performance degrades over time. This forces data to be written directly to disk (write-through). This usually occurs when the initial copy is cached or buffered (either in memory or in the RAID controller's memory cache) and the cache runs out. Follow these guidelines to verify this situation: This is because file copy speeds are limited by storage speed.įile copies sometimes start fast and then slow down. Try the file copy command for unbuffered IO ( xcopy /J or robocopy /J). If you observe slow transfers of files, consider the following
This article provides suggested troubleshooting procedures for slow file transfer speeds through SMB.
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