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Mounting internal and external drives when booted from USB Mojave installer

D

DrBrush

macrumors member
Original poster
Apr 27, 2016
64
64
Hi,

I have a MacBook air I need to sort out, and am looking for some advice.

It has one issue that I think is due to being filled to bursting - with essentially 0 hard disk space. So that it will boot, just, but basically will not function. There exists (somewhere) a TimeMachine backup, but we have moved house and it is one of the hidden casualties that will hopefully resurface somewhere. All of the data is also on an iDrive account, which while providing a last-ditch backup is not where I want to restore data from.

I have created a USB installer of Mojave. What I would like to do is to reboot using the installer disk, and then mount both the internal drive and an external USB drive. Do a simple copy-paste of the data from the internal to external drive and reformat and install Mojave (internal drive of MBA is currently on El Capitan).

Can I do this? Will both the internal El Capitan drive and the external drive mount? Will just reading data from the internal drive when it is only acting as a drive be ok when there is no space to work with? Even if it is slow, can I transfer even a few Gb of data, then delete that data from the internal drive and make enough space to move the rest of the data comfortably?

Are there any better approaches?

Just in case it is relevant I will also note that there is a problem with the laptop not charging. It will "run" (i.e. at least try to boot up so I know it is getting power) when plugged in, but the light on the charger does not come on and the battery will not charge. It is not a problem with the power adapter as the adapter charges another Air, and another charger does not charge this Air. It is not the batter, as I have replace the internal battery, and that did not solve it. I have put this issue on the back burner for now as it could at lease be run as a desktop if necessary once I sort out the boot issue. I know that there are some things I could try to sort out the battery (SMC reset etc) but they all need the computer to boot ok before I try them.

Thanks,

Brush
 
Unless you are talking about a regular drive that happens to have an installer application on it, the USB installer is only that - just enough to install (with a couple of utilities), but not much more.

You can boot the Air from a larger external drive (with a regular file system on it) and shuffle stuff around, and if you can connect to another machine the Air can also be started up in Target Disk Mode, where it just acts like an external drive.
 
Red Menace said:
Unless you are talking about a regular drive that happens to have an installer application on it, the USB installer is only that - just enough to install (with a couple of utilities), but not much more.

You can boot the Air from a larger external drive (with a regular file system on it) and shuffle stuff around, and if you can connect to another machine the Air can also be started up in Target Disk Mode, where it just acts like an external drive.
Click to expand...

No - I am talking about a USB drive that only has a Mojave installer on it. OK - I shall install Mojave on a drive and use that to boot from. I was just wondering if I could shortcut things...

I used to use TDM a lot when everything had a Firewire port - what does TDM work over nowadays? The MBA has USB and Thunderbolt 1, but that's all... My options for viewing over TDM are from either a MBP 2012 non-retina or Mini late 2012...
 
Sure, but interesting how that Apple link specifically states TDM requires TB2. Not sure if I will go that route anyway as I don't have a TB1/2 cable, but if TDM works over TB1, then you would think Apple would say so on that link.
 
"I have created a USB installer of Mojave. What I would like to do is to reboot using the installer disk, and then mount both the internal drive and an external USB drive. Do a simple copy-paste of the data from the internal to external drive and reformat and install Mojave (internal drive of MBA is currently on El Capitan)."

You can't do these things with an "installer USB drive" UNLESS you're willing to use the terminal to do so. Too much work for me!

My suggestion:
This will require that you have a USB external drive available (not your installer drive).

What to do:
First, connect the USB external drive and erase it to Mac OS extended with journaling enabled, GUID partition format.

Next, boot from the USB installer with the external drive connected as well (hmmm... can you do this with a MacBook Air? How many USB ports does it have?)

Now, open the OS installer and install a copy of the OS onto THE EXTERNAL DRIVE (NOT onto the MacBook itself).

When the install is done, BOOT from the external drive (reboot and hold down option key CONTINUOUSLY until the startup manager appears, then select the external drive with the pointer and hit return).

You can now get booted to the finder from the external drive.
Now you can start moving stuff "off of" the internal drive, at least until you get about 10% free space.

Then, try rebooting from the MacBook again -- it should work better.

HERE'S AN ALTERNATIVE course of action:
Can you get booted to internet recovery?
(command-option-R at boot)
If so, you could skip the flash drive installer.
Just connect the external USB drive, and have internet recovery do the OS install onto it.
Then, boot from the external and "do surgery" on the internal drive.
 
This will be my approach I think. I was being lazy and trying to avoid the extra step, because I recalled that I had read somewhere that you could individually mount other drives when booted into the Install Mojave USB. But if you need to use the Terminal, while I am all up for learning new things you are right - why take the complicated approach when I can simply make a boot external USB drive from the very same installer.

The MBA does have two USB ports, but I will set up the new external boot disk using my MBP anyway (old 2012 so two USB-A ports as well).

Thanks for the advice.

Brush
 
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