Dell PowerVault ML6000 - Manual (Page 287)

Chapter 12 Installing, Removing, and Replacing
Permanently Removing 9U Library Expansion Modules From an Existing Library
Dell PowerVault ML6000 User’s Guide 287
3 Disengage the Y-rails so the modules can be unstacked safely.
1 Front Y-rail
2 Rear Y-rail
3 Y-rail (this end up)
4 Squeeze here to release