Moving photos to flash drive or external drives to optimize storage on iMac

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Moving photos to flash drive or external drives to optimize storage on iMac

I have been getting a "Memory Full" notice on my iMac lately. Rather than buy more storage I was thinking that my photos are the likely biggest file and I can move them to a Flash Drive however I tried using a 32G Lexar and while downloading I got the message that the drive wasn't large enough. I can handle that but I have no idea how large I will need. I currently have approximately 14,000 pictures as well as about 100 videos. I'm less concerned with the videos as I can lose them and not be concerned but I'm guessing the quantity of images is the main problem.

Is it time for a separate Hard Drive for external storage? My concerns here are both the need for more storage on the computer, but also that if I do use a Flash Drive or an external HD will I still be able to utilize the storage device to create a slide show as I currently do using the pictures on my current HD. The issue with them is that I need to have a copy of all the images in a folder on my desktop to create my randomized slide show as was once easily possible with iPhoto, but no longer so with Photos. The work around has been great but at the cost of storage space.

[Re-Titled by Moderator]

Original Title: Photo File size for Flash Drive

iMac 27″, macOS 15.6

Posted on Oct 7, 2025 4:06 PM

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Answer 1

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Richard.Taylor

Level 6

16,303 points

Oct 8, 2025 7:36 AM in response to Paul Tabone1

First, flash drives are notoriously slow and undependable. They are great for quickly transferring stuff from one computer to another, or for copies of pictures on a digital frame, but you should never trust anything important to one.

Since you have an iMac, using an external drive is a terrific choice. Get two. You need one for a Time Machine backup. And you need the other for stuff on your iMac that's taking up lots of room.

If space is a problem now, it will never get better. The only way to alleviate a storage problem is to have more storage in the form of an external drive. Photos does lots of background scanning and syncing and stuff, so the drive it's on should be fast-- an SSD s ideal. It should be formatted in Apple's APFS format using the Disk Utility app. Time Machine backups can be done on a cheaper, slower drive, if cost is a problem. A TM drive should have twice the capacity as your iMac.

Because I use a MacBook and haul it around, I keep my Photos Library on the internal drive and other stuff on a small, 1 ounce, portable SSD that I can easily carry. The Photos Library, for me, stays on the internal drive, because it doesn't like being repeatedly connected and disconnected as happens with a portable drive. But for a Desktop computer, there is no real downside to keeping the Photos Library on the external drive. Pretty much anything you can do on the Mac's internal drive you can do on a fast external SSD.

A desktop drive is usually a bit less expensive than a portable version, but that may depend. Get drives made from reputable companies.

You can just drag the Photos Library from the Pictures folder to your external Drive. The old one remains--Don't delete it until you're sure the external is working as you expect. You will need to designate the external drive as your System Library in Photos' Settings>General, and you can connect it to iCloud there if you want.

Does it really say "Memory Full?" Memory is not storage, and it doesn't usually get "full" -- limited memory slows things down, mostly.

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