We are using a SymStore on a fileshare and I recently noticed, that there are over 100k transaction files in the 000admin folder. About 95 % of these files have an .deleted extension, because they have been already deleted.
So is it safe to delete those files to save some space and make life easier for NTFS?
TLDR: no, in general it is not safe to delete these files.
Long answer: SymStore can do different operations, main of which are "add" and "delete". On every operation it changes files in 000Admin folder, adding there information about what was added or what was deleted. Later this information can be used by other SymStore commands, like "symstore query" command, for example. If you delete some of the transaction files from 000Admin folder - it means history of commands will not be accurate anymore and "symstore query" can't work properly.
Of course, if you are 100% sure you don't use such commands and you just need to store pdb files - you can delete files in 000Admin. However, you should understand some functionality of SymStore will not be available to you anymore.