The hint is: there is not enough space-use compression?

No, don't use it. Fast, fastest compression. High, maximum pressure compression.

If "No" is selected, compression is not applicable, and compression is performed according to the normal image.

If you choose fast, you can simply compress it, but first make sure that the GHO image file is the fastest. This will make the file larger, but it will be the fastest.

If the selection is high, the speed of making a GHO image is the slowest, but the GHO file is the smallest and the compression ratio is the highest.