9edd1e4c_NTFS__Logical_Disk_Manager__Type_of_Container_
[Extend:] Adding to the end of stripe "W:" would need at least two disks. The partition on disk 3 could be extended, or the same amount of space could be used from disks 2 or 4. [Add Mirror:] Mirroring would also require at least two disks, different from the ones that the stripe is already on. By mirroring onto two different disks, it will build a fault tolerance for the volume. [Type of Container:] 
Stripe
S i m p l e
S p a n n e d
S t r i p e
M i r r o r
S t r i p e w i t h p a r i t y
M i r r o r e d S t r i p e ( n o t s h o w n )
NTFS: Logical Disk Manager