Best (and quickest) way to back up a large Photos library?

"....what do you actually mean by "system version"?

On some versions of macOS I had crashes, when I tried to export too many originals at once. i don't remember which versions. Right now, on Ventura I can export very large amounts without crashes.

? And when you say "available memory"-

this is referring to the RAM, the program memory, not the storage on your hard drive. I noticed, that the amount of images I can import or export at once, is less on my macs with only 16GB of RAM than on my macs with a larger RAM.

Q. is this: can I not just copy and paste the "file" from Finder and copy that onto a different external hard drive, and have that as my backup, or will that not work because essentially the file will only be able to be opened using the Photos App? I believe I am right in thinking so but again-just want the reassurance that I am understanding all of this.

This will depend on your use of iCloud Photos. If your photos are currently syncing with iCloud and you have "Optimize Mac Storage" enabled, the Photos Library, not all original photos stored locally. The library is incomplete, some photos will only be in iCloud, and the copy of the library on the external will also be incomplete.

But if you are not using iCloud Photos and all photos have been downloaded to the library on your internal drive, you can copy the complete library to the external drive (don't use copy and paste, the library is too large - use drag and drop). How ot prepare the external drive is described here: Move your Photos library to save space on your Mac - Apple Support

But to see the photos in the copy of the Photos Library on the external you will also need the Photos.app.

One final point: when exporting the way you're suggesting....do we end up with .jpg format photos? In other words, these photos will be able to be opened "normally" and not needing the Photos App to open them, correct? If so, then to some extent, I already do have backups of (most) my photos because after a holiday, for example, I download the photos taken (download from iCloud) and import them onto my external hard drive.

M suggestion has been to export with File > Export > Export unmodified originals. Then the exported files will be in the format you have imported them to Photos. If you imported JPEGs, you will be exporting JPEGs and do not need Photos to browse them.

Depending on your system version and the available memory or the file system format of your external drive it will be better to do the exporting also in smaller chunks.

But it is easier to this in Photos for mac than by downloading from the website, because we can select or chunks of export items systematically.

In Photos you can create a smart album to select the photos you want to export systematically. I am using a smart albums based on the range of the capture date, for example:

With a smart album like this you can select large date ranges at a time and know exactly, which photos have been exported.

To export, I am using this preset to export the unmodified originals:

This way the original filenames created by the camera will be preserved, the metadata will be saved in XPM sidecar files, where I can recover any changed dates, locations, keywords, titles. And the list of exported files will be structured by the Moments. All photos taken at the same place on the same location will be grouped by subfolders named by the date and the locations are easy to retrieve from this archive.

Once the archive exists, I only export the recently imported image files. I will find them with a smart album like this:

This album will find all items imported after the date of the last backup, because I am checking for the "Date added" and not the capture date.

I am directing the exported originals directly to yearly folders, structured like this, for example:

When you say...."but if you are no using iCloud Photos"....did you mean "not using the Photos App"? because my assumption was that we are *always* using iCloud photos? In other words, any photos taken on iPhone are auto. uploaded to the cloud. In any event, yes, I am using iCloud Photos...all of my photos taken on my iPhone are auto. synced to the cloud, so essentially, everything is in the cloud in iCloud Photos.

It is not compulsory to use iCloud Photos. We can use Photos without uploading the photos to iCloud. We can have many Photos Libraries (Create additional photo libraries in Photos on Mac – Apple Support (UK)), and one of the Photos Libraries can be enabled to sync with iCloud Photos.

For example, I am using a smaller library with only my favorite items and my most recent photos to sync my photos with iCloud Photos to all devices. But I have many other photos libraries on external drives as a backup and an archive of all photos. I rarely need to connect the external drives - mst of the time the selection of my photos on the internal drive does suffice.

The Photos Library we want to use with iCloud Photos need to be enabled as the system photos library (see: System Photo Library overview in Photos on Mac – Apple Support (UK). Other applications can only access the photos in the System Photos Library.

Because only one of your Photos Libraries can be syncing with iCloud at a time, it is complicates to backup the iCloud Photos Library, if it is optimized and not all original image files have been downloaded from iCloud. The copy will be useless because of the missing originals. We would have to make the copy the iCloud Photos Library and sync it with iCloud, bat then our main library would no longer sync with iClud Switchin iCloud back and forth between large Photos Libraries iss not feasable, because each new syncing wouls tage weeks.

I am keeping my System Photos Library so small, that it will fit on my internal drives and all mobile devices, without having to fall back on to the Optimize Storage Feature. So I can copy the library freely to have a backup. Time Machine can backup the library as well. And on my iPhone and iPad I am always having access to my photos, even when I temporary do not have an internet connection.

You're welcome. Good Luck! 😊