How can I install elementary OS in a partition of an external HDD?

Question

I am trying to install elementary OS inside an external HDD, so I can take it with me anywhere and use it any time I need it. I have done many Linux installations before on this HDD, but using the whole memory. What I need now is to install it only in a small part.

I mean, there exists two well differentiated formatted partitions inside it, one with 650GB which I want for common storage purposes (like a normal pen drive), and another one with 100GB where I want elementary OS to be installed, totally separated from the other 650GB. The problem is that when elementary OS asks me where to install everything, it does not let me to do it on the correct partition...

It shows sda disk (Mac OSX), sdb, sdc (the HDD), and inside it, sdd1, sdd2 (650GB partition) and sdd3 (100 GB partition)

How can I solve this? And what should I choose where it asks for where to install the bootloader so I can boot it from any PC?

Answer 1

Letting the installer to "decide and install everything" means it will also do the partitioning for the whole physical drive. You can simply manually "install everything" on sdd3 (the 100GB partition) by making it the / partition and not create a swap partition.

Though for that setup, I recommend repartitioning the single 100GB partition into three separate partitions with 4GB for swap, 48GB for /, and the remaining 48GB for /home and manually set them to their respective mount points during the installation.

For the MBR, as @lemonslice has mentioned, use the MBR for the disk drive, which is /dev/sdd.

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Source: I have the same exact external HDD setup but with 2TB of storage and more complicated partitioning (with LVMs and encryption)

Answer 2

You should install to the MBR of your external disk drive, which is /dev/sdd in your case.

This way you can boot from your external disk after you have selected it from a one-time boot menu.