I notice that the answers are very different. I think it is because we read your question in different ways. Please make things more clear:
- Either edit your question to make it more specific, so that we understand what you want,
- or, if one of the answers is targeting exactly what you want, you can accept it and that way let us know (and if you let me know that my answer is not what you want or need, I can delete it to decrease the confusion for other people.)
Your [original] question and my answer
How can I setup an internal SATA SSD such that it boots an Ubuntu
installer ISO image ? This would be much faster than using an USB
You can treat a SATA SSD (internal SATA or external eSATA or connected via a USB adapter or box) just like a USB stick, if the tool you are using is allowing it.
And you are right, it is much faster than using a USB stick.
The naive approach to
dd the image file to a disk partition and then
grub to chainload this partition does not work. Why not ?
Which is the key feature for booting an ISO image that a thumb drive
has but an internal drive misses ?
I have done it with
dd. So it works, but if you use the simple cloning method, there will be a terrible waste of drive space.
But there are several methods to create a persistent live drive with a partition for persistence, where you can use the remaining drive space 'behind' the cloned image, or create a dedicated partition table.
I have done it many times and can confirm that it works. I have also created persistent live drives with
mkusb, edited the partition table (when booted live-only 'to RAM' from the drive itself) and created an installed system in the drive space made unallocated. (It is even possible to overwrite the live system completely, when you install the system, but if you make a mistake you have to start from the beginning, so I would not recommend it.)
You can also use other methods to boot via grub.
The following links describe methods that work, if you want to setup an internal or external SSD such that it boots an Ubuntu installer ISO image.
How is it easier to make a persistent live drive with Ubuntu 19.10? - you can use
mkusb-sedd directly for an internal target drive because
mkusb-plug needs a removable target drive
Ubuntu on a USB stick - boot in both BIOS and UEFI modes