There are four disks scanned by fdisk -1, while there are five scanned by vxdisk list.
Sdb is a virtual physical disk, run rm delete command by hand to delete it.
Suggestions and summary:
What vxdisk list sees is the DMP floor of VXVM sends inq command to the device, if the command is returned, the disks are in position. The other disk sdb scanned by vxdisk list is related to a real physical device sdb. The device cannot be seen in fdisk -1, but you can send inq command to it, and returned successfully. The kernel of the problem is you can send inq command to the disks which cannot scanned by fdisk -1. The scan results of vxdisk list and fdisk -1 are diffrents is lead by dmp of vxvm, and it is normal. But read and write command cannot be sent.