Open Stack

Dear,
i have some issue about: create more than 16 cores in one server.
i already change QUOTA at my Project by nova-manager project quota --project=xxxxx --keys=cores --value=64
and my flavor format is: 8vcpus 8mems 0Disk
                                          1vcpus 1mems 0Disk

my physical machine env.
Host Server: Ubuntu 12.04 openstack essex
                       CPU: 24Cores MEM:64Gmems
Node1 :         Ubuntu 12.04 openstack essex
                       CPU: 24Cores MEM:64Gmems

Host instances distribution: A: 8vcpus 8mems 0Disk
                                                B: 8vcpus 8mems 0Disk
Node1 instances distribution:  C~L: 1vcpus 1mems 0Disk => 1*10 =10vcpus 10mems

Frist Test: 
1.nova-manager service disable --serivce=nova-compute --host=Node1
2.create new instances by 1vcpu 1mem in Host Server ----> Fail

Sec. Test:
1.nova-manager service disable --serivce=nova-compute --host=host
2.nova-manager service enable --serivce=nova-compute --host=Node1
3.create new instances by 6vcpus 1mem in Node1 ----> PASS 10+6=16Cores
4.create new instances by 1vcpus 1mem in Node1 ----> Fail
5.Delete step3.4 instances. and create new instances by 8vcpus 1mem in Node1 ----> Fail

could someone give me a hint to solve this issue???

Edward