(I'm assuming by "local data directory" here you mean the "storage" directory. The local Zotero database, which is also in the data directory, is necessary for Zotero to function.)

If Zotero File Storage sync is set to download files only "as needed" in the Sync pane of the prefs, you and other group members won't need to keep the whole set of files locally. There's not currently any way within Zotero itself to delete downloaded (or locally added) files, though, so you'd have to manage that yourself, for example by doing a search for PDFs within the 'storage' directory. In the future Zotero may offer ways to delete the associated local files from within Zotero or to keep it to a certain amount of disk usage by removing non-recently-used files (while keeping the attachment items in place so the files can be redownloaded).

That's right, as long as you delete the actual files on disk, not the attachment items in Zotero. And you'd want to double-check that those files were in fact on the Zotero servers by making sure you can view them on zotero.org. They should be there if you've synced, of course, but occasionally people run into glitches.

Thanks Dan!

I encountered a similar problem, even though I have all the pdfs stored on my computer. When I copied a collection folder from my library to a group library I own, the attachment items that are visible in the reference list were copied over, but the actual pdfs were not (filled blue circles in my library became empty blue circles in the group library).

So when I try to open the pdf in the group library, I get error "The attached file could not be found...". The "Locate" button in the error message of course allows me to navigate to the corresponding file and copy it to the group library, but this is not practical as there are hundreds of pdfs to deal with.

If I copy the items from my library to the group library one by one rather than inside collection folders, then the attachments seem to go along and can be opened in the group library. But I am not able to drag the pdfs from my library to the group library as long as the corresponding parent item exists in the group library.

Is there a more elegant solution to getting the pdfs to the group library than deleting all the items that are already in the group library and then copying them back again with the pdfs in place?

OK, thanks. I tried dragging entire collections again, and this time it worked.

With a setup like hannatuomisto, is it possible to update the attachment icons in the middle pane (blue circles) so that they accurately reflect when an attachment has been deleted locally?

I do not understand how to copy items from "My library" to the Group Library. Can someone please tell me the steps? I've looked at the documentation and can't figure out how to do it. Thanks much Holly