RAID striping can be implemented via hardware (such as a RAID SCSI controller) or via the OS (AIX). If implemented via hardware, you can probably go into the SCSI controller set-up or bios program to see the RAID stripe size.
If RAID is implemented in AIX, obviously you would check the disk management facility for AIX used to do the striping. I am not an expert on AIX, so maybe someone else can tell you how to do this if you have software RAID.
Hardware RAID (SCSI controller) is more efficient than software (OS) RAID.
The stripe size is set for a particular array, and not the entire OS.
Stripe sizes are typically about 32K or 64K (in my experience), but extent sizes for DB2 are expressed in number of pages (typically 4K), so don’t confuse the two. In other words a 64K stripe size would be 16 extents (64K / 4K page size). Extent size can be an even multiple of stripe size.