I would like to store my Photos library onto an external USB Flash drive. I have found other articles explaining that it was possible to store a Photos library onto an external USB SSD or HDD and would like to do the same on a USB Flash Drive.

The reason for the above is that a USB Flash drive (i) holds enough space,(ii) is MUCH smaller and (iii) can always be plugged in.

In the case that this is possible I have some specific questions and would very much appreciate if someone could shed some light on this.

  1. Is it possible to use a USB Flash drive to store a Photos library and access this library when I use the Photos app?
  2. Does performance greatly suffer or is acceptable when using the Photos app (browsing or editing pictures) with the above configuration?
  3. Would it be suggested to format the USB Flash drive to another more Mac friendly format? If yes what would be suggested?
  4. On the other hand, in the case that I were to use an external HDD using USB 3.0, would the performance be equal or below to using a USB Flash drive?
  5. Lastly would I need to remove the external drive from the exclusion list from Time Machine in the case that I wanted Time Machine to back it up?

Thanks in advance if anyone can provide some feedback.

Much Appreciated!

  • Performance is like tastes in food. Everyone's opinion is equally valid. I'll answer the objective issues and link to other answers that cover how to move files to slower storage than the main boot volume. Feel free to ask a follow on question on specific benchmarked needs.
    – bmike
    Commented Sep 6, 2015 at 17:05
  • Performance aside, I wouldn't trust a Flash drive to store any valuable data, ever, if I didn't have a solid backup somewhere else. They are just not reliable, & when [not if] they fail, they fail catastrophically, with no hope of recovery. I get through hundreds if not thousands of them for work, which may skew my perception, as we treat them as disposable data carriers, & that's the best they appear to be, over time.
    – Tetsujin
    Commented Sep 6, 2015 at 18:28

1 Answer 1


You should format the secondary storage as OS X extended and journaled. That ensures the mount of the device is quick and you don't have to wait for a full fsck cycle if it unmount uncleanly. The speed penalty of journaling is almost un-measurable. The speed penalty for not journaling is huge each time you mount the drive.

You want OS X style ACL and permissions, so don't choose FAT or other formats if you care about speed and no bugs/issues.

Here is guidance on the actual move and measurement tools to check drive speeds if you don't simply want to time the Photos app once you've moved the folder.

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