The ChunkSize property was added in Q1 2013. You can set it to the desired size of bytes, Telerik recommends that you set this value to be more that 3000 because when it is less than 3000, the uploading progress may not work correctly.
The DisableChunkUpload property is available as of Q3 2012. By setting the DisableChunkUpload property to true the RadAsyncUpload can upload files in one chunk. This functionality is useful in custom handler scenarios.
For example, when a custom handler is used and the Process method is overridden the uploading file is not saved to the Temporary folder until the the base method of the Process method is called. This allows users to save files directly into a database without saving them on the server.
When setting the DisableChunkUpload="true" property the Silverlight and Flash modules are automatically disabled. This will turn off the multiple file selection in the appropriate browsers.
The DisableChunkUpload property of RadAsyncUpload influences the way files are being saved in the temporary folder on server. In case the property is not set or it is set to "false", temporary files are named under the convention timestamp + actual file name + actual file extension. In case the property is set to "true", files receive random strings for both their name and extension.