We are aware that file sharing is significantly slower than it needs to be to provide a native-like experience and are approaching the volume mount performance issue from multiple angles. We hope to have major performance improvements in the coming beta releases. Watch the changelog for news!
I recommend comparing our filesystem sharing performance to VirtualBox’s and VMWare Fusion’s performance as all of these applications are performing approximately the same actions to achieve the result. Additionally, I recommend using a larger block size than 1024 bytes as each block must traverse the hypervisor and file system daemon and then be acknowledged before the next block can be written. Right now, we have a block limitation of a little under 32k which we are currently working to increase. We are also working on improving file system access latency.
Thanks for your feedback on the Docker for Mac Beta!