How do I backup my iPhoto Library to an external hard drive and keep my photos grouped by their events?

Question

How can I backup my iPhoto Library to an external hard drive and keep my photos grouped by their events?

Answer 1

I have attempted to make sure my iPhoto library has been backed up on the external hard drive and that it is safe to delete some events from my internal hard drive
You need to think this through.
Time Machine is a back up application. It keeps a rolling back up of the data. It's called rolling because it means you can revert to the data you had on a specific date and time. But that's not eternal, and as time goes by, and your drive fills up, older backups are deleted. So if you delete Events on your Mac they will - eventually - also be deleted from the Time Machine back up.
If you wan tot archive data hendon't use Time Machine for that job. Here's how you might archive an iPhoto Library:
Make sure the drive is formatted Mac OS Extended (Journaled)
1. Quit iPhoto
2. Copy the iPhoto Library from your Pictures Folder to the External Disk.
Now you have two full versions of the Library.
3. On the Internal library, trash the Events you don't want there
Now you have a full copy of the Library on the External and a smaller subset on the Internal
Some Notes:
As a general rule: when deleting photos do them in batches of about 100 at a time. iPhoto can baulk at trashing large numbers at one go.
You can choose which Library to open: Hold down the option (or alt) key key and launch iPhoto. From the resulting menu select 'Choose Library'
You can keep the Library on the external updated with new imports using iPhoto Library Manager