Hello all, Hoping someone has been through the same, and can confirm. Started original iPhoto library on my MBP, years ago. A while thereafter, also bought a Mac Mini, to be used at home as the media manager. In thinking I would spread the load a bit (for backup purposes as well), I copied the MBP iPhoto library, onto my Mac Mini. As time passed, occasionally the wife's iPhone was plugged into the Mac Mini, and her photos were fed into that iPhoto library. Ditto my daughter's iPad Mini. Then we came across old digital backups of photos (pre Apple days), and chucked these into the Mac Mini library. Result: 60% similarity between MBP and Mac Mini iPhoto libraries, with the other 40% differing between the two. iCloud: About a month back, I finally took the plunge on iCloud Drive, and upgraded to the 200GB option. Switched on iCloud Photo on all of my devices (iPad Pro; MBP; iPhone and Mac Mini). At home, the upload speeds are slightly slower than moss growth. At work, blazing fast. So, whilst the Mac Mini has been chugging along for weeks, slowly slowly pushing 5/7/9 GBs of 89GB up to the cloud, the MBP (connected at work) did it in 4/5 days... When I log in at iCloud.com, I see (under albums) a iPhoto events library, which has been fully uploaded. This is presumably the MBP library. Thereafter, I recently noticed a 2nd iPhoto events library, which has greyed-out albums in it, mimicking the events on the Mac Mini iPhoto events library. This has yet to be populated. I think I only noticed it recently - don't think it was there from the beginning. Regardless, after all this time, I was expecting something to be in there already, since the Mac Mini has been chugging away for weeks already... So I'm hoping that all that has happened is that the faster upload speed of the MBP, probably got things in 1st, and the Mac Mini was first sorting that library out, and only thereafter, started laying the groundwork to get its library up into the cloud... Hence the 2nd, greyed-out iPhoto Event library... My query: It suddenly occurred to me that I don't recall seeing anything specific about 2 Photos libraries feeding into ONE iCloud account... Surely it must be possible? I do recall all the advice about merging libraries, and now I'm wondering if I've committed some cardinal sin here, of having two devices upload a different library, simultaneously? Was I to have first merged a 'new' mega-library on the Mac Mini, of both Mini and MBP, and then uploaded ONLY from the Mini? Or will I be ok? Is the system smart enough to know which library is going where? And if so - is it blindly going to upload duplicates, or will there be some type of management going on? Simply put - can I (a.) upload into iCloud from TWO Photos libraries; and b.) If so - is the expected behaviour to have TWO separate iPhotos events folders? Will everything duplicate, leaving two 'carbon-copies' of my Mini and MBP Photos libraries in the Cloud, which will then be pulled down to all my devices again? Would really appreciate some confirmation/explanation in regards to the above... Appreciate you reading! TL: DR >> Can/should I upload TWO Photos Libraries (from a MBP and Mac Mini) into a single iCloud Photos (drive) simultaneously, or will doing so cause a tear in the time-space continuum?