Using a Micro SD Card on a MacBook for Dropbox

A little over a year ago, I wrote an article that documented how I was using an external drive with Dropbox. Over the last year, I’ve been trying several methods in the hopes of finding the perfect solution.

This article is where I will be documenting my use of a Micro SD card to store Dropbox content. I’m using an adapter that takes a Micro SD card and allows you to stick it into your MacBook’s SD card slot and sit flush with the edge. I’m using this BASEQI adapter and this PNY 128GB card and it looks like this:

2016-05-28 10.09.37

I started researching Micro SD cards and their speed, but quickly had to just say, “Well, this is probably as fast as it is going to get”. My Micro SD card is what is called a “U1” card. Here is a table that shows the different speeds of SD cards, taken from along with all the logos you will see on the SD card and it’s packaging:

Screen Shot 2016-06-04 at 3.34.53 PM.png

As it turns out, it wasn’t as fast as it was going to get, since I got a U1 Micro SD card which is 1/3 as fast as the U3 Micro SD card.

It is worth noting, when looking at these speed levels, the difference between the lowercase “b” and the uppercase “B”. When you see 100 Mbps, that means Megabits per second. But there are 8 bits in a byte. When you see 100 MBps or 100 MB/s, that means MegaBytes per second, or 8 times faster.

Now that we know that my new U1 Micro SD card is going to operate at 10 MegaBytes per second, let’s compare this to the SanDisk USB drive I was using before… That used “USB 3” (yes, there is a difference between USB and USB 3 – USB 3 is loads faster). Since my U1 Micro SD card is 10 MB/sec, and USB 3 was a minimum of 100 MB/sec, I already know that this is going to be at least ten times slower.

However, USB 3 can burst up to 640 MB/sec, so while my 10 MB/sec Micro SD card is guaranteed to be at least 10 times slower – it could be 64 times slower…

USB 3 can range anywhere between 100 MB/sec to the theoretical maximum of 640 MB/sec. So right off the bat I know that my Micro SD card won’t operate as fast as the previous USB 3 SanDisk drive. If you can find a Micro SD card that is U3, you’ll be at least three times faster than a U1 Micro SD card.

In summary:

  • USB 3 – 640 MegaBytes per second
  • U3 Micro SD – 30 MegaBytes per second
  • U1 Micro SD – 10 MegaBytes per second



But I’m using this for Dropbox, so does any of this even matter?



On day one, it felt like it was going to matter, and that this Micro SD card just wasn’t going to work. Moving large volumes of files from the USB 3 drive to the Micro SD card took a really long time. And when I say a really long time, I mean that it took the better part of a day (closer to 18 hours than 1 hour).

I also felt like it was slowing the whole MacBook down. Over the next few days I decided to change Dropbox’s Selective Sync for a couple of folders. I wanted to have as much of my Dropbox on my SD card as I could, so I began downloading large, multi-gigabyte folders to the Micro SD card that I didn’t have on the old USB drive.

This took longer than I expected. Moving Dropbox from my USB drive to the Micro SD card was one thing, but downloading just one 2GB folder from Dropbox took the better part of a day on very high-speed internet.

I started out using exFAT as the file format on the Micro SD card, but quickly reformatted that to OSX Extended since I had read that it made a big difference in speeding up access to an external drive.

I asked over on StackOverflow to see if the format of the SD card played a big role in the speed of the card. I was thinking that the internet speeds weren’t the problem, so possibly it was an IO issue on the card, but the consensus was that the formatting of the drive doesn’t have as much to do with the drive speed (ie: USB3 is faster than Micro SD U3 is faster than Micro SD U1).

I’d like to experiment with exFAT, OSX Extended, and OSX Extended Journaled, running speed tests on the drives with each format, but I’m worried about how much time it will take. 🙂

As of today, I’ve synced everything that I have room to sync from Dropbox. I have about 5GB free on my 128GB Micro SD card. But now that I’m done with the most of my syncing, the MacBook is performing normal again. I intend to leave things for a while and see how they are doing, but as of now, it seems like this is an acceptable solution once you have a chance to get everything synced up.


UPDATE: June 5, 2016

I’ve been experimenting with something that I was confident was going to be a failure: running applications from the Micro SD card. I had done this on the USB 3 drive, so I thought I would give this a chance on Micro SD as well.

The first application I moved over was pretty lightweight and low-usage: flux. Flux helps to adjust the color of your screen so that you get warmer tones as you get later into the night. That worked out very well, and I never even noticed a change in the way things loaded.

With the success of Flux under my belt, I decided to do something drastic: I moved Google Chrome over to the Micro SD card. Google Chrome is my primary web browser, so I was sure this would be a total bust, but… here it is, a day later and, believe it or not, I’m updating this blog post in Google Chrome on the Micro SD card. I don’t really understand why, it works exactly as fast as when it was on the SSD hard drive.

I’m going to try moving more CPU-intensive apps over to the Micro SD card. It would be interesting if something like Photoshop or Garageband could run off of the Micro SD. I kind of doubt that would work, but I’ve obviously been wrong before. We’ll see.

UPDATE: June 8, 2016

For the past few days, running Dropbox on this Micro SD card has been working out perfectly. So I decided to add applications to the Micro SD card to see how well they could run on it as well. I found a problem that you should be aware of…

I took an overnight trip and took a lot of photos on my smartphone; I knew these were going to need to get synced up with Dropbox, so when I came home, I opened up my MacBook and watched to see what would happen.

Well, it turns out that Dropbox went to work right away to sync the new photos to the Micro SD card. HOWEVER, I had just moved Google Chrome to the Micro SD card. As it turns out, while Dropbox was downloading the new photos, Google Chrome wouldn’t even load.

Now then, I need to go back and clarify exactly what is happening here, because this setup does in fact work pretty well if you aren’t doing what I am doing.

So I was trying to use Dropbox with a U1 Micro SD card as the storage location, AND have applications that I would run directly from the same U1 Micro SD card to save space on my MacBook’s internal SSD.

As long as Dropbox isn’t syncing data and downloading files, this works flawlessly. I have been able to even run Google Chrome from the Micro SD card without any noticeable change in speed. But while Dropbox is downloading data, any application on the Micro SD card will not operate at an acceptable speed.

UPDATE: September 22, 2016

Pay attention to the speed of the Micro SD card, or you will regret it later. Here is proof:


I’m just trying to copy 650MB to this Micro SD card and it says it is going to take 17 minutes. This would already be done if I was using the USB 3…

UPDATE: October 27, 2016

Lately I’ve been thinking that my MacBook isn’t getting a good wireless signal over in this part of the house. I don’t know for sure, but I had a hunch that maybe the kids were watching Netflix and with all the streaming going on, maybe it was slowing down my MacBook…

I’m inclined to say I was wrong about that.

I happened to look at the storage used on the Micro SD card for Dropbox and noticed that I had less than 3 GB left on my 128 GB card (they generally say that you should reserve 10% of any hard drive or disk – and that’s on any computer…)

It’s kind of like riding in a van: if there are 3 or 4 people in your minivan it isn’t a problem. But if you have 8 or 9 adults in your minivan, it is packed. You’re going to feel every movement of the person next to you. And the person behind you will feel like they are breathing down your neck.

The same is true for this Micro SD card. Remember that _MY_ Micro SD card is the slowest of the bunch, so your’s might be faster, but if it is over 90% full, you’ll want to upgrade. I’m looking into it now. 😀

UPDATE: June 15, 2017

I know that I’ve mentioned this above, and that I mentioned it in the previous post, but I feel like it needs to be restated and given some emphasis:

If you are using Dropbox on a Mac, You absolutely must format your SD card as one of the following:

  • OSX Extended (Journaled)
  • OSX Extended (Case-Sensitive, Journaled)

These formats will be a problem:

  • MS-DOS (FAT)
  • ExFAT

Here is why: the Mac operating system creates “hidden” files. Hidden Files just means that they start with a dot, but the Mac operating system creates “dot underscore” files for each file you create. For example, if you have a file called IMG_5000.jpg, the Mac will also create “._IMG_5000.jpg” to store information about the original file.

If the drive format is OSX Extended, then Dropbox seems to kindly ignore all of the hidden files, but for some reason, if the drive is MS-DOS or ExFAT, Dropbox will copy all of these files up. Then, when you are browsing Dropbox online or on another computer, you’ll see all of these files. Imagine you have 1,000 photos in your Camera Uploads folder. Well, guess what? You’ll first have to scroll past 1,000 “dot underscore” files before you see any of your real photos.

It is a real pain, but if you find yourself in that situation, remove Dropbox from your computer, reformat the drive as OSX Extended, then re-install Dropbox and download your data again. There just isn’t any way around it. You’ll also have to manually delete any dot underscore files that are lying around.

There are tools for deleting these, but since that is pretty destructive, I’ll just leave you with the searches you’d want to do to clean things up. Do this cautiously though.


  • How to recursively remove dot underscore files OSX
  • How to use dot_clean on removable media
  • Script to remove all dot underscore files OSX