FileVault Encryption

Actually Filevault works differently on the 2018+ Macs which have the T2 security chip or the M1 CPU. With these Macs, the data on the internal SSD is always hardware encrypted. Turning on Filevault for these 2018+ Macs just adds a password to the mix which only takes seconds to do. Here is an Apple article with the details (very vague details as usual with Apple):

Encrypt Mac data with FileVault - Apple Support

For older Macs, Filevault encrypts the whole volume and not just the parts which hold the data. The speed depends on the size of the drive, the health of the drive, the type of drive (HD or SSD), and how much the drive is being used. Plus with laptops the encryption process only occurs while the Mac is running on a power adapter.

6i2n4k wrote:

But when I turned on FileVault, it only took minutes to encrypt 100 GB. Is this correct? I'm using an iMac (24-inch, M1, 2021, 12.4 Monterey)

That's certainly possible if you are only encrypting the internal drive.

If it's related it should be fine.

It's not just because it's an internal drive. There are many factors involved. How fast the machine is, how fast the drives are, how external drives are connected, etc.

You're welcome.

6i2n4k wrote:

This explanation explains everything I was wondering about. Thank you!

Apologies. I was trying to avoid explaining everything. 😎