FileVault slows down USB stick dramatically

lancastor

macrumors 6502a
Original poster
Jun 25, 2011
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I have read many opinions that FileVault encryption on Mac OS doesn't slows down read and write speed in a big amount.

I have used BlackMagics Disk Speed Test to compare a fresh formatted stick with and without encyrption.

Not encrypted stick: Read 55 Mbit/s / Write 132 Mbit/s
FileFault encrypted stick: Read 29 Mbit/s / Write 77 Mbit/s

Is this a normal behavior that FileFault dramatically slows down the read and write speed?
 

Weaselboy

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Jan 23, 2005
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Is this a normal behavior that FileFault dramatically slows down the read and write speed?

I have had the same experience when using FV on USB thumb drives. My theory is the controllers on those things are low end and can't handle the overhead of the encryption. I have tried even supposed "high end" USB keys and they are all horrible with FV turned on.

What I have done that seems much faster is to make an encrypted sparse bundle image and put that on the USB key, then put any files inside the encrypted image. That seems to keep the speeds up pretty well.

https://support.apple.com/en-us/HT201599
 
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grahamperrin

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Jun 8, 2007
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… My theory is the controllers on those things are low end and can't handle the overhead of the encryption. …

If encryption is not a feature of the drive then to the controller, it's simply data (e.g. blocks); decryption will be performed by the Mac.

Sparse bundle disk image: smart. I guess that for some USB flash drives, the size of the bands (within the bundle) + OS X = superior (to Core Storage) for performance.
 

Weaselboy

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If encryption is not a feature of the drive then to the controller, it's simply data (e.g. blocks); decryption will be performed by the Mac.

Yes in theory... but you can test it yourself. Format three or four USB keys in encrypted format and I suspect you will find what I did... that the transfer speeds go straight to hell.
 
Last edited:

grahamperrin

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Jun 8, 2007
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I don't doubt that performance can be worse with Core Storage.

@Weaselboy maybe think of it like this: the USB flash drive can not know whether Core Storage or DiskImages framework or whatever is in use …
 

Weaselboy

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I don't doubt that performance can be worse with Core Storage.

@Weaselboy maybe think of it like this: the USB flash drive can not know whether Core Storage or DiskImages framework or whatever is in use …
Understood... but the data is written to the storage chip differently with core storage and these low end controllers found in USB keys just don't seem to be able to deal with that.
 
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