I have recently upgraded my pool of mirrors to double my storage space and, upon rebooting the machine, I received this email from the FreeNAS server:

freenas.local kernel log messages:
> GEOM_ELI: Device ada0p1.eli destroyed.
> GEOM_ELI: Detached ada0p1.eli on last close.
> GEOM_ELI: Device ada2p1.eli created.
> GEOM_ELI: Encryption: AES-XTS 128
> GEOM_ELI: Crypto: software
> GEOM_ELI: Device ada1p1.eli destroyed.
> GEOM_ELI: Detached ada1p1.eli on last close.
> GEOM_ELI: Device ada3p1.eli created.
> GEOM_ELI: Encryption: AES-XTS 128
> GEOM_ELI: Crypto: software

-- End of security output --

The interesting thing is that I have never enabled encryption for this pool, so this looked weird.

Apparently, these lines appear in your logs even if you haven’t enabled encryption, according to DrKK on the forum:

You’re going to get these messages, period.  Your pool is almost certainly NOT encrypted.  Your CPU, however, supports hardware crypto, but believe me, if you were encrypting your pool, you’d know, because you’d have to decrypt it in order to mount the pool when you restarted the box.

See the manual on encryption.  You can ignore these crypto messages on startup.  Your pool is NOT encrypted until and unless you take the trouble to set up the whole thing.

So even if you see this message, it doesn’t mean your FreeNAS box has any encryption enabled. As to why this would appear in the logs anyway, it’s anyone’s guess.