36h is a pretty long time... guess there will be more details needed:
- What's below the VG? (Software RAID, hardware RAID?
- Which controllers, which settings (ie what RAID level) are you using, was the RAID set fully initialized when you created the VG?
- what disks are you using?
- how's the load of your system, what do the io statistics (graphs provided by DSS) show?