Copying Huge Photos Library to External Drive


A couple of us started getting nagged by our computers about running out of disk space. We’re both running Mac High Sierra; 15% free disk space is required, which on our 500 GB ssd drives is 75 gig.

After cleaning off files and running clean-up utilities (lost my browser history; I’m sure that was a space hog <eye roll>), I still had only about 50 gig free. Then I found a huge Photos library on each machine—over 300 gig each.

No biggie. I threw money at it by buying a couple 4 TB external drives and started copying the files over. Which would work until like 50 gig from the end or something like that and then quit, complaining about running out of application memory. With no apps running but Finder.

I even tried using Terminal to copy the files. I don’t know why I thought it might work—I was opening an additional app. Turns it’s wonderfully easy to copy files in Terminal: type cp at the prompt then drag the file into the window then drag the destination into the window and hit Return.

But it didn’t work. I’m not really sure why.

The google machine told me that High Sierra has a bug in the copy huge file process. But I have an older computer running Sierra with lots of disk space. So I ran an ethernet cable between the two computers and tried a basic Finder copy from one to the other.

I realized I’d initiated the copy from the “wrong” computer and stopped the process to initiate it from the other computer. I ran Disk Utility on my old computer hard drive just to play it safe and it found an unrepairable defect. Even in Recovery mode, it was unrepairable. And the machine wouldn’t reboot from Recovery mode.


I <3 Macintosh computers. I just had to boot into Recovery mode again (Cmd-R on bootup, until you see the Apple). Used Disk Utilities to erase the hard drive, then reinstalled the system.

Now I really have space on that hard drive.

This time I got smart and used FTP to move the huge Photos library over to my Sierra computer. I set up the High Sierra machine with the huge Photos library as an FTP server: Just go into System Preferences, Sharing, and turn on Remote Login. You might need to go to Users and Groups to add the user who will remotely log in.

It’s easiest if you can remotely log into the High Sierra as the owner of the Photos library file; otherwise, give the user Read/Write access. (Read Only is not good enough to write the file to another computer.)

I used wireless networking (so that the High Sierra machine was still in touch with the world) and it took forever, but it worked. I was able to FTP the huge Photos libraries over to the Sierra machine and then out to external drives from there.

The High Sierra machine was barely affected by the FTP get going on, at least for basic email/web surfing use. The Sierra machine chugged away.

After I deleted the huge Photos library from my hard drive, I ran Disk Utilities, which ended by saying I had like 50 gig free. What?! One of its pieces of information was that there was 350-plus gig free (300-some purgeable).


I brought up About this Mac, the Storage tab, and saw it almost full then sort of sparkle, eventually ending up with 350-plus gig free. Success!

Neither High Sierra computer complains about low disk space.

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