Error: The partition map needs to be repaired because there’s a problem with the EFI system partitio

[musicmic]

Hey everyone,

Something odd happened and I was hoping to get some help. Basically i had/have a stable 10.10.2 yosemite build. gryphon z97, 4790k, samsung pro ssd.

I had a 2tb WD black storage drive hooked up via sata format exfat and it was working/mounting fine. I backed up data to it. One day after no changes had been made to system it wasnt mounted. Of course I checked all the basics like making sure all plugs connected, verifying and repairing disk, and checking my board design routed all sata connectors through the main intel chip and not a separate marvel chip needed a driver.

I looked up this issue and others have had it except I dont see a clear solution anywhere. A similar thread is here:

Anyways I can see the drive in disk utility but its greyed out. At first I could repair disk and it would say it fixed it but upon restart same issue with the EFI partition map error but now it doesnt even fix it just says backup data and repartition. I tried mounting the efi partition through efi mounter than running repair disk but still no avail. i really dont think the drive is bad. Something is going on in the boot stage...
??

 

[musicmic]

One other thing. Under diskutil list it says he partition is microsoft basic data. Im not dual booting. Always been just doing the same thing. Booting to yosemite. Its so weird. Noone has had this issue??

 

[musicmic]

so found a workaround solution.
looks like exfat doesn't play nice with osx and tends to easily get corrupted. So if you are using this format to keep the drive easily accessible to many os's than you may have to run this code a few times. worked for me.

fsck_exfat -d disk0s4

Main boot region needs to be updated. Yes/No?
yes
​

after this the drive should be able to mount

credit here.