Some newer AIX servers come with SSD (Solid State) disks in order to increase performance and energy efficiency. You need to be running at least AIX 6.1TL06 to support them.
SSD disks cannot be mixed with traditional disks and cannot share the same volume-group. The LVM commands such as mkvg have been updated to include SSD-only options e.g. mkvg -X SSD
To see if you are using SSD:
# lsdev -Cc disk | grep SSD
hdisk9 Available 01-08-00 SAS RAID 0 SSD Array
hdisk10 Available 01-08-00 SAS RAID 0 SSD Array
hdisk11 Available 01-08-00 SAS RAID 0 SSD Array