I had a case last year where customer hdd had a lot of bad sectors.
I cloned it on new drive, then i did scan clone drive in R-Studio but i could open only few files.
R-Studio also reported errors on filesystem when i tried to access into partition.
After a lot of working i found that drive was partially encrypted with FileVault, i really don't know why it was partially decrypted, i suppose that probably customer tried to unlock drive by disabling encryption but operation was interrupted at certain point due to bad surface.
This i think would explain partial decryption of a FileVault encrypted drive.
In my case, only files that were located in the first 50 GB of surface were readable but folder structure was all readable (no strange symbol on folders name).
After all i mounted clone drive into virtual machine with WMware, i emulated El Capitan OS, but partition was not readable by Mac OS, see pic:
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not readable drive in mac virtual machine.jpg [ 163.81 KiB | Viewed 9119 times ]
Finally i decrypted all drive by following this guide:
https://derflounder.wordpress.com/2011/ ... oot-drive/then i repaired few missing and damaged folders by using DiskWarrior.
All data were successfully recovered