Can you revert to iPhoto with 10.10.4 with its library on an external drive?

What version of iPhoto do you have?

iPhoto remains as it was, Photos is an entirely different app.

Basically if it's iPhoto 11 ( that's v9.x.x) then it can be upgraded. Other wise no.

Assuming you had iphoto v9.x.x then there is no need to revert with TM. You can upgrade it as follows:

Go to the App Store and check out the Purchases List. If iPhoto is there then it will be v9.6.1

If it is there, then drag your existing iPhoto app (not the library, just the app) to the trash

Install the App from the App Store.

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Sometimes iPhoto is not visible on the Purchases List. it may be hidden. See this article for details on how to unhide it.

http://support.apple.com/kb/HT4928

One question often asked: Will I lose my Photos if I reinstall?

iPhoto the application and the iPhoto Library are two different parts of the iPhoto programme. So, reinstalling the app should not affect the Library. BUT you should always have a back up before doing this kind of work. Always.

I never had iPhoto 9.x.x so it won't be listed in my App Store

If you did not have any version of iPhoto '11, version 9.x.x., then downgrading back to MacOS X 10.7.5 will not help to upgrade iPhoto. It will allow you to run your old iPhoto version, but Apple stopped selling iphoto from the App Store, so you cannot purchase if 9.6.1.

So I guess I don't have much options other than to go back to 10.7 and enjoy it for what it is...

You can buy iPhoto '11 from Amazon as part of the Life '11 package. With Apple's for update downloads you can update this to iPhoto '11, version 9.4.3. https://support.apple.com/kb/DL1650?viewlocale=en_US&locale=en_US

That is the last update that has been published outside the AppStore. It will suffice to run iPhoto '11 on Lion and Mountain Lion, but not on Mavericks. All later updated for the dos recent system versions have only been available from the App Store.

I can understand why I have two Photos library but don't see why there is such a large discrepancy between the sizes, ~470MB vs ~2GB?

That is hard to say, because we do not know how you created the Photos Libraries. If you open an iPhoto Library in Photos it will create a new library, approximately the same size as the original iPhoto Library. If you enable iCloud in Photos with the option "Optimise Mac Storage" the size will be smaller for that library, because the original image files will be stored in iCloud and only smaller versions kept on our Mac.

The iPhoto Library might be larger than the migrated Photos library, for example, if it contains an iPod Photo Cache.

I'm thinking its because of the hard links created by the new app...However, when I look at my pictures on Photos, it doesn't look like all of them are there...

Did the migration get interrupted by a crash? So that photo might be missing?

Would it make sense for me to use iPhoto library manager and have all libraries merged and then use a software, which I need to search for, that can locate duplicates and delete them???

iPhoto Library Manager requires that you have a working version of iphoto installed.

What you could do would be to open all your iPhoto libraries in Photos to create Photos versions of them. This way you can open them and compare the Photos inside in Photos and see, if you still have all your photos.

Photos does not support to merge libraries, but if you invest into PowerPhotos (Fat Cat Software – PowerPhotos), you can browse and compare multiple Photos libraries and search for duplicates. PowerPhotos is the successor to iPhotoLibrary Manager for Yosemite and Photos.

jsa wrote:

Would it make sense for me to use iPhoto library manager and have all libraries merged and then use a software, which I need to search for, that can locate duplicates and delete them???

Yes - and IPLM can merge iPhoto libraries ignoring duplicates - and it is one of the better solutions to finding duplicates in iPhoto libraries

LN