I recently lost a lot of files, due to a hard disk error, but still have a Perforce folder containing files from a particular project. Trouble is, it's not the actual project files, but some kind of Perforce storage format, with files ending in ",d" and ",v"
Is there any way I can restore the original files from what I have?
I imagined Perforce would be able to open the folder as a depot, and I'd simply be able to get the files into a new workspace, but I can't see any way to open an existing depot. I tried editing the depot's "Storage location for versioned files" to point at the folder, but the depot still shows as empty.
I only used Perforce briefly (comparing it to Git) so I don't really understand how it works. Any help or advice would be much appreciated.
The thing you're missing is the database (the db.* files), which need to be in the server root (P4ROOT) when you start the server. If you don't have database files in P4ROOT, the server will create an empty database on startup. The database is the source of truth for a Perforce server, so if it's empty, the server is empty.
If you have a checkpoint (a file called checkpoint.N) and/or journal file, that contains the metadata you need to reconstruct the database; recover the server with p4d -jr checkpoint.N journal, and then you can use the p4 depot command to make sure the Map of your depot(s) points at the directory where your archive files are, and use other commands to inspect the actual files (start with p4 verify to see which files are in the database but missing/corrupted in the archive backup).
If you only have the archive files but no database (and no checkpoint or journal to recover it from), you're in a more difficult spot since the database is what maps the archive files into the actual depot structure (e.g. it includes all the copy-by-reference pointers that constitute branches in Perforce). However, you can extract the contents of the archive files one file at a time using conventional tools; the ,v files are in RCS format (use the co command to retrieve their content), and the ,d directories contain regular old .gz files, one per revision.
Using the deep magic to synthesize a database from the archive files on their own is also a possibility, but the RCS/CVS conversion scripts are so old I'd expect a lot of fiddling to be required to get them working with a current version of Perforce.