Note: For this to work your system must be below or at 1.80 for the 1.80 debug update, and below or on 2.01 for the 2.15 debug update. Just use the next version up from your current firmware version for the retail update. Also NOTE this only allows for non-functioning Debug menus.
Download a debug PS3 firmware and place it in USB stick, and start the update. This will copy all the debug firmware files to the PS3's HDD-A.
After copied the PS3 will restart and you will see the normal update menu which prompts you to click the (PS) button to start update. Do NOT update your PS3, but power it off.
Next remove the HDD-A, and place in the second HDD, HDD-B in the PS3.
Download and copy a retail PS3 firmware to a USB stick.
Again as before place USB in PS3 and update the PS3 as normal but when you get to the screen where it asks for you to press (PS) button, do that but stop when it asks you to AGREE to Terms and Condition Page.
While the system is still powered on and on the update screen, REMOVE HDD-B, and insert HDD-A.
After swapping the HDD's continuie to update the PS3 as normal and the PS3 will install the debug PS3 firmware!
Go to the settings and check firmware version and there you will also see the debugging PS3 options
For those who are seeking to do this method with 2 different hard drive sizes, a method has been found:
Originally Posted by ggparallel
Now for everyone with hdd problems, you can do a copy of the whole hdd and make it working. I used the following procedures I have two hdd 60GB and 40GB:
I made a full format of the 40GB hdd and then I used the dd_rescue utility (http://www.garloff.de/kurt/linux/ddrescue/) to recover the 40GB image on the 60GB hdd now I have a perfect copy, and it works of course.
I can do this trick on a ps3 with any firmware update??
There's no point in do this as there is no functionality and it will somewhat cripple the console and no you can not do it on any firmware, sony blocked this little swap trick after 2.42 if memory serves.