Why does FileVault improve disk performance.

[0014]

Out of curiosity I wondered if FileVault on my 2018 MBA with T2 would have a hit on disk performance like it did on my 2015 MBP.

The bonus with the T2 is the encryption/decryption is instantaneous. Unlike the hours it would take on my MBP.

However to my surprise I got slightly better disk read/write speeds with FileVault on rather than off and wondered if anyone knew why? No other reason than curiosity as the difference in terms of usability is negligible and only noticeable in a Speedtest. This is on MacOS Catalina Dev Beta 2 although would have expected that to impact performance rather than improve it.

FileVault OFF

FileVault ON

 

[chabig]

It should make no difference. Probably what you observed is normal variability from test to test. Run your test hundreds of times and you'll discover that it's the same with or without FileVault.

 

[0014]

It should make no difference. Probably what you observed is normal variability from test to test. Run your test hundreds of times and you'll discover that it's the same with or without FileVault.

I thought that. But I did 5 on each and the figures were roughly the same +/- 20MBPs

 

[Weaselboy]

I thought that. But I did 5 on each and the figures were roughly the same +/- 20MBPs

That is odd because on T2 Macs even with FV not enabled, the data is already encrypted. Turning on FV just adds a password to the encryption.