I had a power failure while using two of my hard drives (two WD Red 4 TB, each one nearly full, HFS+ data only, no OS on the drives) in a dock.
Since then I was able to recover almost all my files with DiskDrill but some are corrupted, some have lost their name and directory.
Since I have nothing more to lose here, I put my hands in it.
I am trying to rebuild the GPT with testdisk, but I failed several times.
So I've already written few times on gpt with testdisk, I've also tried the method using testdisk to find sectors of partition and pdisk to write them, but it failed.
Now I am trying again with testdisk and wxhexeditor.
I am looking at every occurrence of "HFSJ", the first one match the sector testdisk had found 529400 (271430664 in hex).
But I can't find any EFI partition. Is there a way I can fix that? And rebuild GUID partition scheme?
Here is the result of sudo gpt -r show disk2
:
start size index contents
0 1 PMBR
1 1 Pri GPT header
2 32 Pri GPT table
34 529366
529400 7812357952 1 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
7812887352 1149783
7814037135 32 Sec GPT table
7814037167 1 Sec GPT header
Follow-up: I tried what you recommend with the following result:
diskutil unmountDisk /dev/disk2
Unmount of all volumes on disk2 was successful
sudo gpt remove -i 1 disk2
disk2s1 removed
sudo gpt add -i 1 -b 40 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk2
disk2s1 added
sudo gpt add -i 2 -b 409640 -s 7813365344 -t 48465300-0000-11AA-AA11-00306543ECAC disk2
disk2s2 added
diskutil verifyVolume disk2s2
Started file system verification on disk2s2
Verifying file system
File system check exit code is 8
Error: -69845: File system verify or repair failed
Underlying error: 8: POSIX reports: Exec format error
this is beyond my understanding!
Best Answer
Initially partitioned with Disk Utility (as GUID pt, 1 partition, HFSJ) I would expect the partition tables of your WD Red 4 TB disks to look like this:
with the EFI = 409640 blocks and the empty default Apple spacer of 262144 blocks. All aligned to the 4096 Byte physical block size the resulting HFSJ partition starts at block 409640 and has a size of 7813365344 blocks.
You may just test this by removing the current partition (below I assume the disk identifier of the external drive is disk2 - use the disk identifier you have found in your environment):
If asked don't initialize any volume.
Now verify the volume:
After further investigations it turns out that one of the two external disks contains an additional recovery partition. After adding a 3rd partition like this:
and the help of Disk Warrior (to restore broken file systems) both main volumes of the external disks have been salvaged.