Security is an ever growing concern and encryption is a great step to achieve this. This page will provide a comparison between encrypted data and a normal single drive and what impact it will have on the performance. Not all NAS feature Full volume and Shared Folder encryption, but I will test what is available.
Shared Folder Encryption
Encrypting a single shared folder does affect performance quite a bit and we see drops in performance of up to 70% in some of the tests. We still get results that you can work effectively from.