I have stacked 100's of 3'5 and even 5 and 12 inch drives without noticing any problems. But the other day I moved 2 2'5 inch drives for cloning to use on a laptop and media device and since capacity was different I wanted to make sure they were the same physical size. So All I did was align them to see if they matched. Both were WDC drives, 1 being one of those video storage units and the other a regular hard drive. Now I was able to clone an image onto the video storage drive and put it in the lap top and it worked fine. The regular hard drive which was in the lap top and working fine, when hooked up to the desktop showed pending sector write errors during clone and failed. Checking the drive showed banks of errors.. 2 blocks would be fine but then the next 2 or 3 would be bad.. Seems to be where the motor of one hard drive was slid across the top of the other caused the markers to demagnetise. I have many times cloned these same hard drives. Never had any problems but this was the first time I had stcked 2 of them to check the sizes. I know the magnets inside the drives are strong but usually they are held in place with a rod whoch stops the magnetic fields from causing problems. Looking at some other 2'5 drives it seems similar to 3'5 drives only smaller.. But it seems the thinner case does not stop magnetic interfearences and might destroy the drive sif you are not careful about external magnets. So just saying, unlike stacking 3'5 drives ontop of each other which does have pretty strong cases, doing the same with 2'5 drives might cause a disaster.. I haev seen storage racks but they have a tray in between each of them. Which might be the safe way to stack them.