How to install El Capitan on a flash drive?

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How to install El Capitan on a flash drive?

I would like to install El Capitan on a Sandisk 128 GB Extreme Pro flash drive to use an alternate startup disk for my Mac Pro or MacBook Pro. I have found instructions online to make an El Capitan Installer out of the flash drive but the only thing you can do with it after that is to use it to install OS X on other drives. You can't startup and run from it like you would your primary startup drive.

I have the 6.2 GB "Install OS X El Capitan.app" and "InstallMacOSX.dmg" on a couple of the three HDDs I have in my Mac Pro, but I have not been able to figure out how to install a copy of El Capitan (which is the OS I am using) onto the Sandisk.

Any help would be appreciated.

Posted on Feb 14, 2020 12:51 PM

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Answer 1

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Eau Rouge

Level 8

42,554 points

Feb 14, 2020 6:05 PM in response to Russ G

First you need to make sure the Sandisk USB is formatted correctly so it can install the OS.

If you can boot your mac up, insert the 128GB USB to your mac. Open Disk Utility from your

Applications/ Utilities. In the left hand column select the Disk, not any indented Volumes,

(see screenshot below)click Erase. Give the Disk a name, Format: Mac OS X Extended (Journaled),

Scheme: GUID Partition Map., click Erase.

Now that the disk is properly formatted try installing El Capitan to it.

Things might work quicker if you move the Install OS X El Capitan.app to the drive your

MacPro is booted too. Double click on the Install app after it opens follow the on screen

prompts till you come to the section where you choose the destination disk, select

your 128GB flash drive and continue with the installation.

Using a USB stick as a means of running an OS is not a great idea, it will be incredibly slow.

And completely pointless on a MacPro. The MacPro has 4 internal bays for different drives

each of which you can put separate OS's on drives/ partitions.

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Answer 2

Russ G Author

Level 1

70 points

Feb 14, 2020 2:22 PM in response to Niel

Well, I have gotten that far, but I get an error message. After I get the error and try to restart the computer it just hangs out a blank white screen.

After I get the error try to restart the computer just hangs out a blank white screen.

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Answer 3

Russ G Author

Level 1

70 points

Feb 14, 2020 6:27 PM in response to Eau Rouge

Thank you.

I had actually done all this a few times and the installer would hang or I would get an error message. Finally, the installation was successful.

I was not creating this USB startup drive to use with my Mac Pro which has 3 internal drives, but rather a MacBook Pro where I may not always have the luxury of another alternative startup disk in the event of an emergency. The Sandisk Extreme Pro 128 GB flash drive, as I understand things, is an SSD, unlike many smaller USB flash devices, and much faster. I have only run my Mac Pro for a short while off this USB drive but it seems pretty snappy...I can't complain at all about speed.

Thanks again.

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Answer 4

Eau Rouge

Level 8

42,554 points

Feb 14, 2020 7:09 PM in response to Russ G

All flash drives are SSDs and have been for years. The read speeds on a USB3.1 interface can be up to 420MBs

a second and write speeds unto 380Mbs a second. The more you use the disk and it fills the performance will

drop.

In the first line of your original post you mentioned,

I would like to install El Capitan on a Sandisk 128 GB Extreme Pro flash drive to use an alternate startup disk for my Mac Pro or MacBook Pro

That is why I said that it is pointless for you to create the USB for use in the MacPro.

I still think it would be a better idea to have an external hard drive as an emergency drive for your MacBook Pro.

Another idea as you have a MacPro, is to have one of the drives in it with an emergency El Capitan partition

on it that if something happens to your MBP you can take the disk with the emergency El Capitan on it and place it in a

HD dock or enclosure and connect it to your MBP.

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Answer 5

Russ G Author

Level 1

70 points

Feb 14, 2020 8:08 PM in response to Eau Rouge

Thanks again.

You are correct as to what I wrote. I cannot for certain recall right now why I included Mac Pro with MacBook Pro when my primary intention is to use the Sandisk with the MacBook for emergency startup. My Mac Pro, BTW, has 3 internal drives as I stated previously. Each of them has an OS installed.

I travel and am away from home for months at a time. When on the road the Mac Pro stays home, so I need something else with me as an emergency startup. I agree with you completely that an SSD would be better than the Sandisk USB, and an SSD is in my future, but I don't have one now which is why I wanted to make the Sandisk a startup drive.

Thank you again so much for your thoughts and the time you have invested to help me!

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Answer 6

Niel

Level 10

727,493 points

Feb 14, 2020 1:53 PM in response to Russ G

Open the installer, and specify the flash drive while setting up the installation.

(178786)

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How to install El Capitan on a flash drive?

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