Large-scale Mendeley-Zotero migration retaining attachments and custom tagging data

TKowalczyk
Hi Zotero community,

I did have a search of the forum prior to deciding to post this, but I couldn't find anything that directly related to the issues I'd like some advice on, if anybody could help.

I am looking at supporting someone with migrating their large (circa 130,000 items) library from Mendeley (the older, recently discontinued desktop app - unsynced) to Zotero.

The overall size of the library with attachments is circa 600GB.

The user has a custom tagging system and so the tag field in Mendeley would need to be retained as part of the migration and be replicated in Zotero.

My questions are:
1) Does the size of the library necessitate any special precautions when undertaking this migration? Would we need a machine with a circa 2TB hard drive to be safe?
2) Would the Mendeley tags be retained in a migration like this?
3) Are there any other considerations we should make with this one? I tried googling and there seem to be a fair few useful-looking open source add-ins and add-ons which could help.

Thanks in advance for any help that anyone might be able to offer.

All best,
Tom
  • dstillman
    edited February 7, 2025
    Zotero has a built-in Mendeley importer that retains essentially all info. Don't use any other option.

    Due to restrictions by Elsevier, this will require syncing all data and files to Elsevier's servers before you can import them into Zotero. You'll need space locally for all Zotero files at import time. (Once the Mendeley library has been fully synced to Elsevier servers, you could offload the local copy to an external disk, though, so you don't actually need 2x the space.)
  • TKowalczyk
    Thanks so much for this reply -- I take it that there'd be no way to do this without syncing up to the Elsevier servers?
  • dstillman
    No. See my link above.
  • TKowalczyk
    Noted. When you say 'don't use any other option', does that include the 'alternative local method' detailed at https://www.zotero.org/support/kb/mendeley_local_import ?
  • adamsmith
    The local option is fine (note that somewhere in the instructions it says "make sure you use Zotero 6" -- that's outdated; both the latest version of Zotero 6 and 7 should be fine)
  • dstillman
    (Recent versions of Zotero 7 actually include support for an additional feature from Mendeley. I've updated the page to just recommend the latest version.)
  • dstillman
    edited February 13, 2025
    @TKowalczyk: To be clear, the "local" method isn't particularly local. For the same reasons as above, you still have to upload all data and files to Elsevier servers first. There's not much reason to use that method these days unless the online importer isn't working (and I have no idea if a version of Mendeley Desktop from 2018 can actually handle all the data in the final version of Mendeley Desktop from 2021, whereas our importer should). Both MD 1.18 and Zotero would have to pull down all data and files from Elsevier servers. Maybe there's slightly more of a chance that, with a huge library, Zotero's importer could get stuck in a way that MD's sync process wouldn't, though if it does we'd want to try to fix that.
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