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.