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Drive in question was my "data drive" and contained:

  • BitLocker encrypted partition (created with Win 10, doesn't contain OS)
  • Ubuntu

I deleted the Ubuntu partitions. What remained was an EFI partition. I deleted this using diskpart on Windows. On Windows disk management the drive was like this:

|---Bitlocker-----|---Empty---|-EFI-|---Empty|

After deleting the EFI partition the whole disk now shows "Unallocated". I'm sure I didn't delete the Bitlocker partition.

What happened? How can I get the Bitlocker partition back online?

By using Minitool Partition Wizard I found the lost EFI partition. I didn't restore it as I fear data loss.

Testdisk analyze says

Bad GPT partition, invalid signature.
Trying alternate GPT
Bad GPT partition, invalid signature.
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This doesn't directly address your question, but on modern EFI/UEFI-based computers, the EFI System Partition (ESP) is required to boot. Thus, unless you had another disk with its own ESP, deleting the ESP was a mistake that would render the computer unbootable. (In fact, even if you had another disk with its own ESP, if your active boot loader happened to be on the ESP you deleted, it would render the computer unbootable.)

I can only guess at what caused the BitLocker partition to disappear, but my two top guesses are a program bug and user error. It's possible there was some combination of the two -- for instance, if the program you used to delete the ESP was so poorly designed as to automatically delete the BitLocker partition when you deleted the ESP, then deleting the ESP might technically qualify as user error, but the poor program design would also (IMHO) qualify as a bug.

As to how to get it back, you might have luck with TestDisk or something similar; however, I don't know how well it would work at recovering BitLocker-encrypted partitions.

  • Thank you. Minitool Partition Wizard found the missing EFI partition. I'm scared to restore it though as I fear losing the data. I will now run TestDisk analyzer. Initial scan shows Bad GPT partition, invalid signature. – Sampsa Apr 15 '17 at 6:11
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    I wouldn't use Test Disk on the drive unless you have a sector for sector copy of the drive, test disk not understanding a bitlocker partition header, is to be expected – Ramhound Apr 15 '17 at 8:16

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