I have been using a 128GB SanDisk Ultra Fit USB 3 device with my MacBook for a while now and have really grown to love having all of my Dropbox available without using up my SSD disk space.

I've recently purchased a 128GB Micro SD card with an SD adapter in the hopes that I can free up a USB slot.

I'm looking for recommendations as to which type of filesystem formatting I should use. I started out with exFAT and felt like it was a little sluggish, so I switched it to OSX Extended (non-Journaled) and I'm not seeing much of a difference.

From what I could find, some people said that using Journaled with a Micro SD card might cause too many writes and could wear out the life of the Micro SD card.

In my case, I'm primarily using Dropbox for file storage and some app usage. I use it with 1Password, but don't do a lot of heavy operations like working directly on Photoshop files.

EDIT: Here are the specs:

MacBook Pro (Retina, 13-Inch, Late 2013)
2.4GHz Intel Core i5
4GB 1600 MHz DDR3

MicroSD Card:
PNY 128GB High Speed MicroSDXC Memory Card (P-SDUX128U160G-GE)

MicroSD to SD Adapter:
BASEQI aluminum microSD Adapter for MacBook Pro Retina 13"

  • 1
    In early 2013 I purchased what was at the time the fastest SDXC Card to hold an image of my OS X built out with all my apps as an emergency boot disk in case the Recovery HD wasn't available on my 2013 MBP. I was disappointed with it's performance as USB3 was much better. Prior to setting it up with an image of OS X I tested read/write times with different filesystems on it and found none to be significantly better then the other. I'm glad its only purpose is an emergency boot device and frankly hope I never have to use it. In the future I'll use USB3 over an SD Card any day. May 31, 2016 at 23:11

2 Answers 2


Your card seems sluggish because it is.

Your particular PNY SD card is rated at up to 60MB/s (megabytes per second) data transfer rate; which is approximately .5Gb/s (gigabits per second)

In comparison, your SanDisk has a read speed of 150MB/s or 1.2Gb/s (SanDisk does not provide a write speed).

Basically, you swapped out a storage medium for another that, out of the gate is at best, less than 1/2 the speed than what you had originally. There is no filesystem that is going to make up that difference.

For reference USB 3.0 is rated at 5Gb/s which is equivalent to 625MB/s.

Format Types

"Using it with DropBox" doesn't have any effect on the file system type you choose to use as DropBox's functionality and performance has nothing to do with where your OS writes its files to. So, the question becomes, which one is is right for you?

  • Use ExFAT if you plan to go between OSes like Windows and Linux
  • Use HFS+ if you plan on only working on OS X and like all the extras you get with HFS+

If you really want (need) Speed

Get an external drive that takes full advantage of USB 3 speeds (up to 5Gb/s) like the WD Passport for Mac or go for a Thunderbolt Drive that will go 10Gb/s


If the SD card seems sluggish, you can try purchasing the "extreme" edition of the SD cards that are rated for professional photographers that need quick writes for RAW photos in fast succession. It costs more, but you get better performance.

The alternative is to wait for Dropbox to release a version that will have placeholders for files stored on the cloud only. The started in May 2016 and I am hoping it will be released soon. This doesn't increase your overall storage, but does allow you to have Dropbox on the SSD and temporarily work with files and release them once you don't need them without having an SD card.

  • Here is the card I'm using, the PNY 128GB High Speed MicroSDXC Memory Card (P-SDUX128U160G-GE) amazon.com/PNY-128GB-MicroSDXC-Memory-P-SDUX128U160G-GE/dp/…
    – brock
    May 31, 2016 at 23:03
  • LOL, yeah that's the one we bought for our Canon camera. That is rated U1, 10MB/s minimum. U3 would give you 30MB/s. You could buy a 128GB SSD for less than $50 these days and a USB to SATA cable would cost you around $10: smile.amazon.com/StarTech-SATA-Drive-Adapter-Cable/dp/…
    – Sun
    May 31, 2016 at 23:09
  • I appreciate the feedback, but it doesn't even address my question: does the format of the filesystem have any bearing on this? Sure, a faster SD card will be faster; I'm interested in optimizing what I have.
    – brock
    May 31, 2016 at 23:14
  • I think the issue really is hardware. Sure, you can use non-journaled without encryption, but you still have a 10MB/s bottleneck: apple.stackexchange.com/questions/116240/…
    – Sun
    May 31, 2016 at 23:21

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