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Optimizing Send/Receive Buffer Sizes in Serv-U  -  KB Article #1438

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Buffer Sizes In Serv-U 7.0+

Serv-U is capable of automatically updating its Send/Receive transfer buffers to optimize connections and transfer speeds. Over the course of a larger transfer on a stable internet connection, a transfer's buffer size will adjust to be as efficient as possible for all transfers on the server. This requires no user input or configuration.

Configuring Buffer Values In Serv-U 6.x

Rather than automatically tuning buffer sizes as new versions of Serv-U do, Serv-U 6.x requires manual configuration of the Send and Receive buffer values. Tweaking these values (Local Server | Settings | Advanced) may improve performance with file transfers through Serv-U. Because of the diverse amount of networking hardware and broadband Internet connections available, it's impossible to provide a general formula for tweaking the buffer size. In addition, different buffer sizes work best for different client connection speeds.

In general, larger values seem to function better for faster, low-latency connections and smaller values work well for slower or high-latency connections. The only way to find the precise setting that is fastest for a given network is trial-and error.

When the "fastest" speed is reached, the number should be moved slightly closer to the norm. In most cases, the range should be between 8-32Kb. Poor data transfer rates may result from settings outside this range. In no case should the value of Send buffer or Receive buffer ever be set above 65535.

Send/Receive Buffer Settings