With the introduction of VMAX 5977 / VMAX AFA these commands are being less important. However if your VMAX has a failed disk these commands may be requested by support to obtain drive information to arrange a replacement.
Symdisk commands: Non-Disruptive
symdisk -sid 4321 list -failed
Provides a high level overview of failed disks in the array. Will provide the director and interface along with the active splits on the disk.
symdisk -sid 4321 list -failed -v
Provides an in depth overview of failed disks in the array. This command will provide additional information such as vendor type and serial number which Dell-EMC support will need to facilitate a replacement drive.