By default, the Catalyst 3850 uses a tftp block size value of 512, which is the lowest possible value. The reasoning behind this default value is to ensure interoperability with legacy tftp servers.
For IOS-XE version 3.3.2 and below, you will have to manually change the block size in the global configuration to speed up the transfer process. The example below is a transfer comparison when using the default block size of 512K versus a transfer using the maximum block size value of 8192K.
ip tftp blocksize 8192
