|All hard drives are subject to failure and/or corruption. For that reason you should ALWAYS maintain backup copies of any data you wish to retain.|
I recommend you obtain an imaging program and use it to create backup images that can be used when necessary to restore data to the same, or a new hard drive. This goes for ALL your data.
I recommend imaging to optical disk (CDR/DVDR) because they are cheap, reliable and not subject to mechanical failure.
In order to consolidate the two drives you would need to: Partition the 250GB drive into at least TWO partitions. Then image the OS files from the 20'GB to a Primary partition on the 250GB. In order for any programs that currently reside on the 250GB the partition they end up on would have to be labeled with the SAME drive letter they presently carry.
All this is somewhat technical and honestly I am not sure will even work. The 250GB partitioning would need to allow the first partition of around 20GB to be set as the active partition. While an experienced user may be able to take the necessary steps I am not sure you have the skill set or the where with all to tackle this.
I recommend that you get an imaging program and image your 20GB hard drive to DVDR disks. These programs compress files so even is your 20GB is pretty full you are probably looking at using no more than 4 single layer 4.7GB DVDR disks.
Then, if your 20GB drive were to die you would simply replace it with a new hard drive and restore the image to that drive. After that everything on the 250GB should work just like before.
One concern I have is this. If your computer is an older model, which I suspect, it may not be 48 bit LBA compatible. What that means is that the BIOS can't properly configure an Internal hard drive larger than 127GB.
If that is the case then your 250GB data is at risk and any internal replacement drive would need to be smaller than 127GB. If your 250GB is using a drive overlay then dat corruption is not an issue but the drive can't be moved to another computer.
An easy way to tell if your computer is 48 bit LBA compatible is to watch the POST screens at the start up to see if all drives are properly identified by BOTH the model and the FULL drive capacity. If the 250GB shows as 127/137GB then you have a problem.
If you don't SEE any POST screens at start up then you need to boot into the BIOS (setup) screens and disable any Logos. Logos are the screen that shows the brand of the motherboard or computer.