Fixing an unmountable drive?

How to use TestDisk to recover lost partition
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keflavich
Posts: 1
Joined: 13 Sep 2016, 16:32

Fixing an unmountable drive?

#1 Post by keflavich » 13 Sep 2016, 16:44

I'm on Mac OS X 10.9.5. I have an 8TB HD with an exFAT partition that is somehow corrupted. Mac OS's disk utility won't mount the drive, so when I attempt to write the new partition table, it fails. When I start testdisk, all of my drives are listed as read only (RO), which prompts the statement:
"Write access for this media is not available.
TestDisk won't be able to modify it."
How can I (re-)mount my HDs so that testdisk can modify them?

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Select a media (use Arrow keys, then press Enter):
 Disk /dev/disk0 - 500 GB / 465 GiB (RO)
>Disk /dev/disk2 - 8001 GB / 7452 GiB (RO)
 Disk /dev/disk3 - 4000 GB / 3726 GiB (RO)
 Disk /dev/rdisk0 - 500 GB / 465 GiB (RO)
 Disk /dev/rdisk1 - 499 GB / 464 GiB
 Disk /dev/rdisk2 - 8001 GB / 7452 GiB (RO)
 Disk /dev/rdisk3 - 4000 GB / 3726 GiB (RO)
testdisk.log shows:

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search_part()
Disk /dev/disk2 - 8001 GB / 7452 GiB - 1953506646 sectors (RO)
     MS Data                      256 1953503999 1953503744
     exFAT, blocksize=262144, 8001 GB / 7452 GiB

Results
   P MS Data                      256 1953503999 1953503744
     exFAT, blocksize=262144, 8001 GB / 7452 GiB
gpt_change_part_type
Change partition type:
   P MS Data                      256 1953503999 1953503744
     exFAT, blocksize=262144, 8001 GB / 7452 GiB
Change partition type:
   P exFAT                        256 1953503999 1953503744
     exFAT, blocksize=262144, 8001 GB / 7452 GiB

interface_write()
 1 P MS Data                      256 1953503999 1953503744

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cgrenier
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Re: Fixing an unmountable drive?

#2 Post by cgrenier » 14 Sep 2016, 19:20

Mac OS X blocks read-write access to disk when a partition from this disk is mounted.
Use

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diskutil list
and

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diskutil unmount /dev/disk2s1
to umount it before using testdisk.
But your title "unmountable drive" seems to contradict my answer...

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