Backup Retention Plan

“On Exit” backups taken by LrC are not required – until they are.  The question of how long to keep them keeps coming up.  The answer depends on several things such as how much disk space you have for such things.  However, some basic principles apply. 

DIMINISHING VALUE OF OLDER CATALOGS (for full restore)

• The farther back in time you have to go, the harder it is to recall everything you’d done since then.
• The farther back in time you go the more work you’ll have to do to replicate what you did in LrC since that backup was taken. 
• Most (but not all) problems that might require a full catalog restore (like catalog corruption, failed drive, stolen computer, Etc.) become obvious rather quickly.  However, some don’t make themselves known for quite some time.
• If you did any folder or image file moving, renaming, deletions, or other “physical” changes after the point the backup was taken the recovered catalog won’t know about those changes and untangling that can be quite challenging. 

So, in general the older the backup the less likely it is that you’ll want to revert to it rather than keeping your current catalog and fixing whatever it is that went wrong (if you can).

LONG TERM VALUE OF HAVING OLDER CATALOGS

Sometimes you want to just “see” what something looked like from a long ago point in time or need to recover data for just some images from an older catalog.   For example, you accidentally removed a folder or collection and need to get those images, with their edits, back. 

For these situations having catalogs that go back farther are quite useful.  In general these ‘older’ catalogs are used as the source for an “Import from another catalog” where you select only specific sets of images rather than reverting to the entire catalog.

A SUGGESTED BACKUP RETENTION PLAN

• Create a new backup folder for each new version of LrC that requires a catalog update so you can easily know which version of LrC the backup is for.  This was less important when LrC was appending version numbers to the end of upgraded catalog names as you could tell by the file name but I still found it useful even then as one had to open each zip file to see the version number in the file name.  Since LrC/14 they no longer include the upgraded version number in the catalog name at all so I’m finding using folders for this even more useful.  On the other hand, many people just use one folder.
• Set the LrC Preference to create a backup every time Lightroom exits.  Then actually take a backup at the end of any day in which you made any changes in LrC.  I suggest shutting down LrC at the end of each day and that’s when I have it do the backup.  This also lessens the risk of damage due to an overnight power failure or power spike.
• Set LrC to store the backups it creates upon exit on a drive which is not in the same housing (box) as where the actual catalog is.
• If you’ve done any major folder structural changes or file renames other than imports in that session make some sort of note on the backup Zip file name or keep a log of major structural changes

Retention Plan:

• Keep all of these backups for 90 days
• For backup ups taken in the 2 years before that keep the first one from each month
• For backups older than that keep 1 to 4 per year (say first one of each year or quarter) forever

The retention durations above are just suggestions.  Feel free to pick different duration spans as desired.  Many people use 30 or 60 days, and 1 year

1.  you do not need to keep ANY of these ‘on exit’ catalog backups on your internal HD.  In fact, if your active catalog is on your internal HD YOU SHOULD NOT put the backups on that same drive.   Move them to an external drive - perhaps the same drive with your recent images which makes that drive an easy emergency grab and go device.
2. Take a look at your preview folder.  If it is large you may want to skinny it down by using the “Limit Preview Cache Size” command or just deleting the folder and let LrC rebuild previews as it needs them.   
3. If you tend to create lots of 1:1 previews for some reason.  You can delete that folder and start over with those as well.

The reason why you may want to keep a few backups, for example one of each month, is as follows. Suppose that you look at some older images, and then discover you did something stupid and never noticed that before. You deleted all keywords from a few hundred images, and because you apparently did that quite some time ago, your recent backups won’t be of any use. Then you want to be able to go back much further, till you find a backup that does still contain those keywords. You can then export these particular images from that old backup as a new catalog, and import that catalog into your current catalog. That way you can get these keywords back without having to replace your current catalog with an old backup.

Look at the dates on the backup files. Decide how long ago do you really need to be able to go back to if your catalog goes bad (a rare occurrence but possible). Delete any older than that. It is best practice as ​@JohanElzenga says to store these on another drive than where your main catalog is but that really depends on how critical your catalog files are. If you run a business based on your photography you really should do that indeed.

Also consider using multiple catalog files for the older images by exporting separate catalog files to the external SSD along the older images and deleting the images from your main catalog in order to keep the main catalog slimmer. If you have a smallish internal SSD (512 GB is really too small for the internal SSD for Lightroom Classic use unfortunately) you can also consider storing the catalog itself on an external SSD. 

Catalogs with names like “Lightroom Catalog-2-v13-3.zip” are catalog backups. You should not store catalog backups on the same drive as your main catalog, because in that case you will lose everything if the main drive crashes. Move these backups to an external drive, and in the catalog backup dialog, point your new backups to that drive as well. You probably don’t need 36 backup either. Decide for yourself how many you feel comfortable with. Keep one or two very old ones, and a few more recent ones.