Never fancied enabling FileVault on previous Macs but now I'm running OS X on an SSD. Is there a noticeable decrease in speed?
Every time you make the computer do something extra, in this case encrypting/decrypting all file access, it will take longer and the machine will slow down a bit.
FileVault 1 did slow things down noticeably, but with FileVault version 2 (Introduced in OS X 10.7 (Lion)) running on an SSD there is no noticeable decrease in reading or writing files. I have this enabled on a 15" MacBook Pro Retina and a 2012 11" MacBook Air. The only time it is noticeable is when you reboot, as it requires a password before starting the boot process.
You may notice that the system is slow when you first enable FileVault 2, since it has to encrypt the whole drive. Once that is done you will probably forget that it is on.
If you decide that you don't agree with me, turning FileVault off is easy enough. You will, once again, have the slow initial period as the whole drive is decrypted.
My own experience with File Vault 2 on Samsung 840 EVO on an early 2011 MacBook Pro running Mavericks is that the slowdown is not noticeable.
I took one speed reading before turning File Vault 2 with
time dd if=/dev/zero bs=1024k of=tstfile count=1024
That showed about 490 mb/s. After File Vault 2 was on and encryption was completed, another reading showed about 315 mb/s. This looked bad, so I did a restart.
Then I took three more readings. They showed 492, 507 and 503 mb/s. I am not claiming that File Vault 2 improved speed. I should have taken multiple readings before turning on encryption, to get an idea of the expected range.
With the data that I do have, I'd say that whatever the penalty is, it's not noticeable.
I just finished turning off Filevault 2. For all who happen upon this thread looking for recent information, here it is.
Corsair FORCE GT 480GB 1.5yrs old. Writes on file vault 2 were under 250mb/s. Noticed the performance degradation.
Secure erased free space repaired disk disabled file vault 2
New write speeds are 438mb/s almost matching the read speeds at 4510 mb/s.
FileVault 2 will show you extreme performance degradation and should be avoided for all who spent the money upgrading to an SSD.