IBM 2104 Model DU3 - Manual (Page 26)

7. Lay the disk drive module on its side as shown in Figure 6. It rests on four blue
supports (not visible in the figure) on the bottom of the disk drive module. This
prevents the disk drive module from falling over and becoming damaged.
Note: It is recommended that the removed disk drive modules be kept in the
sequence they were in before they were removed from the 2104 Model DU3.
8. Repeat steps 3 through 7 for each disk drive module. Ensure that you remove
all the disk drive modules from the 2104 Model DU3.
Figure 6. Disk Drive Module on its Side for Safe Storage
10 2104 Model DU3 Installation Guide