The salt is being saved in base64 getting 22 chars but If it's stored as bytes strings it were only 16 chars. The difference is very great when you have 100K o 1M of users.
The same happens with the hashes which are being saved in hexadecimal, althought the difference is a lot of great.
Digest::SHA512.hexdigest => 128 chars.
Digest::SHA512.digest => 64 chars.
I see what you're saying. I'll try to include this with v3. The problem is that I need to this to be backwards compatible. I'll work it out. Thanks for the tip.