Lenovo ThinkStation P520 Hardware Maintenance Manual page 146

b. Pull the storage drive cage upward. Then gently slide the storage drive cage out of the chassis.
Figure 77. Removing the storage drive cage
6. To install a storage drive cage, do the following:
a. Place the upper edge of the storage drive cage under the front-fan-assembly retainer as shown.
Figure 78. Placing the upper edge of the storage drive cage under the retainer
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P520 Hardware Maintenance Manual