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I have a 4 GB Micro SDHC card and I use a Micro SD adapter sleeve to read it with the built-in SD card slot of my 15" mid-2010 MacBook Pro. It's been a while since I tried to use it, but I just realized that my Mac will always treat it as read-only, no matter the position of the physical lock on the adapter sleeve.

I can't even format the partition because all the options in the "Erase" and "Partition" tabs of Disk Utility are grayed out for the SD card.

Why is the card read-only, and more importantly, how can I write to it?

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I am having this problem with all of my cards, and resetting the PRAM has NOT fixed the issue. I see no solutions on any forums this issue has been posted on, but lots of people saying it eventually just disappeared by itself. I am running 10.8.2 –  user32981 Oct 16 '12 at 21:05
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@Rob, I read on the Apple support forum that for a user, depending on how you inserted the SD card into the slot, it would be read-only or read-write. He said that if you put the card loose into the slot and push from the side closer to you to make contact, it becomes read-write, and otherwise it's read-only. I did it like two times without success but then the problem disappeared on third time. This looks superstitious, but at that point you might want to try anyways. –  zneak Oct 16 '12 at 21:27
    
What MBP model is this? I have a similar issue on MBP Late 2009 –  Max Ried Dec 30 '12 at 12:44
    
It's a mid-2010, I just edited my question to include it. –  zneak Dec 30 '12 at 17:03
    
@zneak WOW your method worked for me the very first time, and this was after me trying all kinds of other ways to no avail. I have a 2011 MBP running Lion. –  Suan Mar 14 '13 at 3:10

8 Answers 8

up vote 6 down vote accepted

In my case, a physical misalignment is causing the read only status. Gently pushing the disk away from the display reliably makes my cards write again.

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Slide the read/write lock to the middle neutral position and retry. I have the same problem sometimes...

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There is a neutral position on an SD card? –  patrix Nov 21 '12 at 7:38
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Sliding the read/write lock to the neutral position works for me. –  user37553 Dec 30 '12 at 14:39
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Weirdly enough, this worked for me (I put the switch about halfway between lock and unlock, popped it back into the slot, and all write options were no longer grayed out). Try it and post your results. –  Nathan Garabedian Jan 1 '13 at 3:16
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I put the lock into the middle position as others mentioned and it, too, worked for me. How bizarre. –  user57071 Sep 13 '13 at 23:18
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This works for me too. Can't believe this will work. –  Nevin Aug 27 at 4:50

Is this problem for all your SD cards or just one. If just one, I would try formatting it in FAT from a PC and then trying that.

I had a USB flash drive that I had installed a Linux distro on and it gave me similar issues on my Mac mini.

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Well I have two Micro SDs at hand and both exhibit the same behavior. I formatted the 4GB one to FAT32 from my digital camera (since that's what I wanted to do anyways) and I still can't write to it. –  zneak Sep 23 '12 at 21:57
    
Also, Linux distributions are generally installed on an EXT filesystem, so my feeling is that you just couldn't write to the filesystem, instead of to the device itself. In my case I can't write to the device at all, and a format didn't fix it. –  zneak Sep 23 '12 at 22:09

The problem spontaneously disappeared for me. I'm leaving this as an answer since it might reassure some people to know that for some random reasons, at some point, things start working again. However, I was not able to pin down a specific cause for it, so I'm not going to accept the answer, in case that at some point someone comes with a rational explanation.

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According to one user on the apple discussion forum, resetting the PRAM should fix the issue:

From Apple KB

  1. Shut down the computer.
  2. Locate the following keys on the keyboard: +Option+P+R. You will need to hold these keys down simultaneously in step 4.
  3. Turn on the computer.
  4. Immediately press and hold the +Option+P+R. You must press this key combination before the gray screen appears. Continue holding the keys down until the computer restarts, and you hear the startup sound for the second time.
  5. Release the keys.

Note: Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.

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I'll try that when I get back home. –  zneak Sep 26 '12 at 21:50
    
The problem spontaneously disappeared today, so I'm afraid I can't verify anything. Still, thanks for the tip, if this happens again I'll try that. –  zneak Sep 27 '12 at 14:31

The tricks above worked for me but less and less so. It feels like a hit and miss and can easily take me 10 tries.

This annoying problem has another potential fix. When I need to get my card into Read/write mode I can do this by taping over the slot of my card where the lock slide is. It does not matter where the lock slide is set to as it will be masked by the tape anyway. This works 100% of the cases. It does have disadvantages:

  • potentially getting tape stuck into the reader (be careful)
  • need to apply it and take it off each time tape
  • might take the paper of any label sticker on the SD card off

I’m actually going to buy a reader because of these disadvantages.

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Another thing to ensure when trying all these 'tricks' is to plug the laptop into a power supply. Because the card reader draws power if the battery is not delivering enough current to the reader it can cause issues. For example, mounting of problematic USB hard disks can be resolved by plugging the laptop to the power supply.

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This sounds more like superstition than like an actual explanation. A card reader acting on NAND Flash storage needs much, much less power than an actual hard drive. My laptop was connected at all times when I had this problem. –  zneak Jul 13 at 16:24

Open Disk Utility, find and select the SD card, then click Repair Disk from the First Aid tab. You should now be able to read and write.

Disk Utility Repair Disk

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Didn't work for me when I had this problem. –  zneak Sep 7 '13 at 16:43
    
Wouldn't the volume be greyed out if it were mounted read-only? I suppose you should be able to unmount it and then attempt a repair, but my guess is the item you have listed as 8.02 GB Apple SDXC Rea… would be grey in the case of this question. –  bmike Sep 7 '13 at 17:49

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