use iPhoto or Photos for books?

You can no longer print books from iPhoto anyway, because Apple stopped the print service for iPhoto books. If you want your books printed by Apple, the new Photos.app as the only option now. Presto Photos can print your iPhoto Books, if you export them as a PDF file.

If you open an iPhoto Library in Photos, the migrated library will not need much extra storage, see this document: Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

In the long run it will be preferable to switch to Photos for Mac, because iPhoto will be less and less supported.

I thought I would link the libraries, instead of importing the same thousands of photos into the new Photos libraries. So the main question is whether or not there's an advantage in migrating all my iPhoto libraries into Photos libraries, or just stick with iPhoto and make my books there. Thanks

Some options: If you also have Aperture, you can easily merge all iPhoto Libraries into one before migrating them to Photos.

The PowerPhotos application makes it easy to manage several Photos Libraries, or to merge them (

http://www.fatcatsoftware.com/powerphotos/

).

I also like the idea of having only one Photos System Library so I can look at my albums on AppleTV, but how would I store 1.5 to 2.0 TB of data on iCloud Library?

That will probably not work, because the largest iCloud Storage plan is 1 TB.

I would merge the older libraries selectively. I kept copies of all my iPhoto and Aperture libraries on a separate drive and merged only the most important photos from each library into my new main system Photos Library. It fits easily onto the internal drives of all my Macs and a 200GB iCloud Storage plan suffices.

You should never do any update or upgrade (or use your computer) without a good, current backup - if you do not always have a good backup you are guaranteed to lose important data

LN

no idea - it sounds like the RAID drive is designed to keep you safe but I've never used it and have no idea how it actually works - i use Time Machine to a Time Capsule and Carbon Copy Cloner to a separate EHD - and do an occasional off site backup (important in case of a disaster)

You probably are fine short of a disaster

LN

I have one Pegasus 6T RAID drive I keep all my iPhoto libraries and iMovie projects.

A RAID is safer than no backup, but if the backplane of your RAID has a problem all internal disks can be unusable at once. Or a power surge could destroy all internal drives at once. I would always keep a copy of my important media drives on a second drive, that is stored in a second location.

You're welcome 🙂