Cannot add a Drive to Indexing Options

Do you use Outlook and do you have any Outlook related files on E:?
See
Indexing of a second drive - Page 2 - Solved - Windows 10 Forums

dortmunder said:

OK, thanks. Is that partition wizard of any use to me then? If not, what else might I try?

Sorry, guess not.

One thing came out of some searching (two actually, but one of them is a bit risky..)

You can delete Indexer VolumeGuid file on affected drive. System will rebuild it.
from admin command prompt type

del "D:\System Volume Information\IndexerVolumeGuid"
and Reboot

Idea came from MS forums. It's not exactly the same problem thou ...
Making backup of that disk is recommended anyway. I usually recommend Macrium. Making image and restoring it is also faster than copying files.. This could be solution, if nothing else works

One more thing you could do @dortmunder. Shrink that D: partition and make new one in empty space. See if new drive would appear in Indexing options. If not, partition table is corrupted. If it appears, move data to new drive and delete old one.

Not elegant solution, but it could work. Making backup and restoring is actually the same, but you get backup of files...

dortmunder said:

That seems like a fairly safe action - you're quite sure the deleted file will be rebuilt with no harm done? Apologies if I sound paranoid and thanks for taking the time to seek answers for me.

No apologies needed. I'm not sure about it, but should be safe.

Was thinking about it some more and another solution seem possible. Permissions could be the culprit. Could be that indexing service doesn't have permission on file system or in registry.

For file system you can check the permissions and compare them to E: drive. for registry go to "Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search" and check that WSearch user has read and write permissions.