MacOS – Importing Photos from Lion to Yosemite Photo Library to External Storage Device

There are two main options which I would go for:

• Put your library and contents on a network volume

  This is the option that I went for on my setup, mainly because I did not consider the second option at that point in time. This option works fine for me — even when the network drops (which is pretty rare): the data transfer pauses and continues when the network reconnects.

  This works fine for my relatively large Aperture library, but I see no reason for this not to work in iPhoto.

  ✓ Easy to set up, just copy your entire library to a network drive and ⌥-launch iPhoto
  ✓ Uses no space on your local machine
  ✗ Possibly susceptible to network dropouts causing problems

• Put your library on your local machine and the contents on a network volume

  This alternative is probably better, but requires that you switch to Aperture. This way, you keep the library on your local machine but the media is stored on a network drive. This means that it uses very little space on your local machine but even if the network drops there is no chance of corruption/etc.

  ✓ Much less likely to have problems due to network dropouts
  ✓ Uses very little space on your local machine
  ✗ Does use some space on your local machine
  ✗ Harder to set up — not as simple as just copying your entire library

There is no way to import an Aperture/iPhoto library except start a new Photos library and have it convert from an existing Aperture/iPhoto library.

I think the best solution would be to start a new Photos library based on your existing Aperture library. Attach your iPhone to the Mac and wait for it to appear in the sidebar in Photos, then import everything it will let you from the phone. Finally, set it as the system library (Photos menu > Preferences > General tab > "Use as System Photo Library") and enable iCloud Photo Library (Photos menu > Preferences > iCloud > iCloud Photo Library).

In theory this should cause the images from your new combined Photos library (old Aperture library + what was on the phone) to upload to iCloud, while also downloading anything in iCloud that does not exist in your new Photos library. And in turn, your phone should download anything new that is uploaded to iCloud.

The step of syncing from your phone directly to the Mac should not be necessary, but is a backup just in case iCloud freaks out with the change in the System Photo Library and removes what you uploaded from your phone. It also saves Photos from having to download any of those photos, assuming it finds them to be duplicates of what's in iCloud.