Use the vmkfstools command to add an extend to a VMFS volume.

-Z --extendfs extention-device existing-VMFS-volume

This option adds another extent to a previously created VMFS volume existing-VMFS-volume. You must specify the full path name, for example /vmfs/devices/disks/vml.vml_ID:1, not just the short name vml.vml_ID:1. Each time you use this option, you extend a VMFS-3 volume with a new extent so that the volume spans multiple partitions. At most, a logical VMFS-3 volume can have 32 physical extents.

Caution

When you run this option, you lose all data that previously existed on the SCSI device you specified in extension-device.