How Dynamic LUN expansion or vxdisk resize work?

First, the LUN is expanded or changed to the new size from the storage end. For the Volume manager to recognize the new size, "vxdisk resize" is needed.
 

When resize operation is issued on a disk (dmname or medianame), VxVM first checks if the disk is part of the imported diskgroup and it is not part of bootdg diskgroup. Disks under diskgroup bootdg cannot be resized. So, the disk has to be online and imported and diskgroup cannot be in Disabled state. All the subdisks from this disk have to be Enabled and active.
 

Next, it checks if disk is not an EFI type disk as EFI disks cannot be resized.
 

Only diskgroups created from versions 4.0 and above are supported.
 

If the disk belongs to a shared diskgroup, then the resize has to be issued from the CVM Master node.
 

VxVM then saves the disk attributes, current public and private region settings. Next, it gets the new disk geometry information and calculates the new disk attributes.
 

Vxdisk resize does more checks based on the new disk attribute values. If disk is share simple/nopriv disk then the resize is not supported. The disk is not the only disk in the diskgroup. If this is the only disk in the diskgroup, -f (force) option need to be specified with vxdisk resize command. VxVM moves the config copies in this disk to the other disk in the diskgroup just to save the config copy during the update operation. Should something go wrong during the resize we might still have a config copy on another disk. This is why VxVM checks if the disk is the last is the last disk in the diskgroup with a valid config copy. If so, it fails unless user explicitly mentions -f option. It also does more check with the on the subdisk and makes sure they fit in the new public region size. During the resize, VxVM quiescent the I/O, updates the private region (header and TOC), recreates the slices if required, temporarily disable subdisks so I/O errors doesn't occur. Perform format and platform-specific changes including, reinit. Update the DA record and resize is done.