vmkfstools command to add an extent to a VMFS volume.
-Z --spanfs span_partition head_partition
This option extends the VMFS file system with the specified head partition by spanning it across the partition specified by span_partition. You must specify the full path name, for example
/vmfs/devices/disks/disk_ID:1. Each time you use this option, you extend a VMFS volume with a new extent so that the volume spans multiple partitions.
When you run this option, you lose all data that previously existed on the SCSI device you specified in span_partition .