It depends on what kind of disk subsystem you are talking about and whether it is controller by AIX or some other means (like EMC disks). If it driectly attached disk, then the LVM (Logical Volume Manager) can be used. Here is a redbook on the LVM:
http://www.redbooks.ibm.com/redbooks/pdfs/sg245432.pdf
32K or 64K are typical for RAID stripe size. Keep in mind that the DB2 entent is in pages so an extent size of 32 is really 128K if you are using 4K pages. So even if the stripe size is 64K, then an extent size of 16 will be a multiple (1X) of the stripe size.