icloud photos not opening on imac

Hi Richard, Thank you very much for all your advice and I now have all my photos on a new hard drive (nothing corrupted). I have now attached it to my iMac and have access to all my photos so all good on that front. My next problem is that these will now not synch to the iCloud. I will attach some photos but basically I have gone to iCloud, clicked photos and synch Mac to on, put in my password (for iMac I presume) ..... then I get the message 'open photos or create a library to use with iCloud Photos ......' ..... I have clicked on photos - they come up (from my hard drive) but nothing else. So I am sure nothing is synching with iCloud. Should I be doing something with the '... create a library to use with ....' - if so I don't know how to do this and would really value your guidance again please. sorry to trouble you again and thanks very much. (also I tried to click 'helpful' and leave a review but every time it says there is maintenance going on - I will keep trying. ALSO - I have just tried to upload the photos for you but get a message that files are too big - not sure what to do but hope my explanation above is good enough for you. Thanks again

Do you have enough room on your internal drive for all the pictures at iCloud.com? If you use Optimize Storage, then they may take up on the Mac only 20% of the total storage at iCloud.

I would create a brand new empty Photos Library, designate it as the System Library, connect to iCloud, and let it fill.

This article has pictures of the settings you need:

Make a New System Library connected to iC… - Apple Community

Macs can have multiple Libraries. Only the one designated as the System Library can synchronize with iCloud Photos. In that article I referred to it says:

Then, on the Mac in Photos>Settings>General, you must make this… Library your System Library. 

In this picture "Use as your System Library" is grayed out, because it already is the system library. Only the System Library can connect to iCloud.

Go to Settings>iCloud and connect this new Library to iCloud.

I really think that your best bet is to make a new empty Photos Library and let if fill from you iCloud Library. That can be way more secure, because all the pictures at iCloud.com have already been scanned and "certified" as not-corrupted. You don't really know what's happened to the Library on your old drive. This new Library that you create can be on the new hard drive.

Be sure to format the new drive as APFS (if the drive is solid state) or Mac OS Extended-Journaled (if it's a spinning drive) using the Disk Utility app. If that gets confusing (as it sometimes does for me) let us know.

The article I mentioned,

Make a New System Library connected to iCloud - Apple Community

has most of the details.

Hi Richard, Again thanks for all your help. I now have a new drive - Sandisk 1TB and all formatted correctly. I have plugged it into my IMac and I have all the photos working pefectly on there. So my next task was to connect to the iCloud and I followed all your instructions ...... now I get this message at the bottom of photos ... ' Restoring from iCloud' - it has been there now for 2 hours and nothing appears to be happening. Once again I would really appreciate your help please. Thanks very much in advance.

It's fine to run a Photos Library from an external drive, but as the message indicates, the drive must be formatted in either APFS format or Mac OS Extended (Journaled) format. The drive must be connected directly to the Mac by cable, not networked, clouded, NASed, etc. Additionally, the drive can not have had Time Machine on it since it was formatted. See this for more:

Move your Photos library to save space on your Mac           

Older OSs didn't check to see if the Library was on ExFAT, and the Libraries would slowly corrupt, becoming totally useless. So it's lucky that Photos stopped you in time!

Libraries can be stored on ExFAT--but they can't be used from there. So you Library is probably OK. But you will need to copy it to another drive or volume. Or, you copied this Library from a previous drive-- is that right? If so, you can re-format the new drive, erasing the copy, and copy again.

To format a drive, you use the app Disk Utility. You choose the drive, the Erase, and then choose enter the name and format:

If your new drive is solid state, then certainly choose APFS (not encrypted or case sensitive. If it's a spinning drive, you can choose Mac OS Extended (Journaled).

Here are Apple's instructions:

Erase and reformat a storage device in Disk Utility on Mac

Keep me informed!

Hi Richard, thank you so much for your reply but i am afraid I am too old and not computer literate enough to understand most of what you have said. I have a 2TB icloud account so all my photos (about 300GB) are on there. My imac is only 250GB so when I bought it the advice was to have an external hard drive - this is 500GB but for some reason unknown to me it suddenly became full 2 days ago which is why I suddenly got the message that it was full and hence I couldn't access my photos. I have today bought another external hard drive 2TB also and am trying to copy my old 500g hard drive with all the photos onto this new 2TB drive. I hope I can then connect this to my imac and then hopefully somehow get my photos back but I am not sure what I will have to do once connected. If the above sounds sensible and correct then perhaps you could help me, in easy stages please, to be able to view my photos again. I am terrified of doing something wrong and losing everything !!!. Thanks again.

Hi Richard, thanks for help and especially diagrams - I followed instructions and on 2nd diagram when I click on iCloud photos I get a message 'iCloud Photos is only available on macOS Standard, macOS Extended and APFS formatted volumes. To check the format of a volume, select the volume that your photo library resides on (I assume this is my new large hard drive where all my photos now are) in the Finder and choose Get Info from the file menu. The type of volume appears in the Format field.' So I have done that and it says ... ExFAT. So I have gone to the message and clicked OK and it just turns the iCloud photos (on 2nd diagram) tick box off again. So once again I have reached a dead end and am asking for your help please. Really sorry again and thanks very much again.