Issues copying MacHD to external drive

[Jane8798]

So my Mac will not start since I installed the latest sierra update- it only shows the loading start-up screen for HOURS. It won’t start in safe mode or cmd v mode either.
I’ve managed to get it in recovery mode and reinstalled sierra and it’s still the same, I’ve also used first aid on disk utilities to no avail.
My next step (since I’m stupid enough not to have used time machine to back up my crap) is to copy my Macintosh HD onto an external hard drive using disk utility and then wipe my MacHD completely so it can restart it, and then copy any files back over to my computer from the macHD copy.
The only trouble is that disk utilities keeps stopping, saying the file is too large- even though it’s only 400gb and the space on my external HD is over 500gb.
I’m so frustrated as I’m not sure what else to do- and I need help! Please!

 

[DeltaMac]

What format is your external hard drive? You can Get Info (Cmd-I) on the external drive. The format should be Mac OS Extended for your purpose.
If instead it is MS-DOS or FAT32 - that's the problem, as FAT32 won't copy any file larger than 4GB, and sometimes not over 2GB in size, and that's when you see that "File too large" error.
The solution is to erase that external in Disk Utility, where you can change the format to Mac OS Extended (Journaled). That will work for your back up then.

 

[Fishrrman]

OP:

If you can't get booted from the internal drive, you need another way to "get booted to the finder". This will make things MUCH easier.

Do you have a USB flashdrive around that is 16gb or larger? (8gb won't do)

If so, try this:
- Get booted to recovery mode
- Connect the USB flashdrive
- In recovery, open Disk Utility
- "Aim" DU at the flashdrive and erase it to Mac OS extended with Journaling enabled. Can you get this far?
- Now, quit DU and open the OS installer
- Aim the OS installer at the flashdrve, and see if it will install a copy of the OS onto it. It will take some time, and the Mac may reboot once or twice.
- If successful, you should see the setup screen (for the OS install on the flashdrive)
- Can you set up a "basic account" on the flashdrive? Just get it so you can reboot to it, log in, and get to the finder.

Can you try this?
If this works, you may be able to get the Mac "booted to the finder" again, and we can go from there.