Time machine encryption vs Disk utility encryption

[edwardjulio]

I have a confusion here, hopefully someone help me to answer my confusion.
I purchased 2 external hard drive( same model). I use my hard drive "a" as a time-machine backup, so I plug it in, go to time machine preferences, select the hard drive, and I choose "Encrypt backup". The first backup was exercised (my data in my mac is about 30gb, it takes 30 minutes for the first back up), and followed by long encryption process( about 18 hours). I noticed that my hard drive a's format change from macOS Extended (Journaled), become macOS Extended (Journaled, Encrypted).

For my second hard drive(let say hard drive b), I intentionally format the hard drive from macOS Extended (Journaled) to macOS Extended (Journaled, Encrypted).

the question is, why my hard drive "a" takes 18 hours to be encrypted, on the other hand, my hard drive "b" takes 5 seconds to be encrypted. At the end, both the hard drive change to the same format anyway.

1. Does it mean, it is better to change the format to macOS Extended (Journaled, Encrypted) before select it as the time machine back up?

2. is my hard drive a faulty?

Thank you!

 

[laurihoefs]

1. Creating a new encrypted volume is much faster than encrypting an existing one, even an empty volume. Disk Utility creates a new volume, Time Machine encrypts an existing one.

2. There is nothing wrong with your hard drive.

 

[edwardjulio]

1. Creating a new encrypted volume is much faster than encrypting an existing one, even an empty volume. Disk Utility creates a new volume, Time Machine encrypts an existing one.

2. There is nothing wrong with your hard drive.

Thanks for your great explanation!