FileVault – Understanding Its Impact on System and TM Performance

filevaultmacosperformancetime-machine

What are the pros and cons, performance-wise, of enabling and using FileVault? Is there any at all, or does it slow a computer down significantly or on the contrary speed it up? Also, what effect will it have on Time Machine-backups (performance-wise)?

Best Answer

(I'm assuming you are referring to FileVault 2 found in OS X Lion)

The folks at AnandTech have run some performance benchmarks on the new FileVault. Quote:

... [described are several I/O tests with and without FileVault enabled, including some charts you might want to have a look at] ...

Overall the hit on pure I/O performance is in the 20 - 30% range. It's noticeable but not big enough to outweigh the benefits of full disk encryption. [...]

[emphasis above is mine]

So to answer your question:

  • FileVault slows I/O down, and it is a measurable decrease in performance. However, I agree with the earlier quoted statement – in that the added security is beneficial, and I use FileVault on my Macbook Air.

  • The answer on the second question is "it depends". The TimeMachine backup process must certainly read a lot of data from the FileVault-encrypted disk, so the reading portion of the backup will be slower.

    However, whether or not the overall backup performance suffers considerably depends on where the bottleneck is in the system – e.g. is it a very fast backup drive, or a very slow backup drive? Is it connected by USB (slower), or Thunderbolt (faster)? If the write speed is terrible, that will govern the overall speed of the backup, not so much the read speed having been reduced a bit. Ergo, it depends.

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