Sir, few days back i was facing issue of controller@lvm in reporting pbm and service will appear down after when i reboot system so to overcome that error after restart i create lvcreate -l 10 -n cinder-volume cinder-volumes after pvcreate and vgcreate no doubt is pbm is fixed..(contin..)

so my question is what is difference now before lvcreate also i was able to create volume and now after lvcreate also i m able to create volume but the only difference is lvcreate helps to overcome that reboot pbm what i mentioned before like controller@lvm is reporting heartbeat pbm

lvcreate only helps to overcome reboot pbm as volume group vanishes after reboot so im in a confusion when i create volume in dashboard the volume size consumed from volume group not logical volume size even though after creating logical volume of some size???

If the volume group vanishes after reboot, it resides on a volatile physical volume. DevStack and Packstack, for example, use a loopback device as physical volume. In the past, DevStack didn't reactivate the loopback device after reboot; perhaps that's still the case.

So, if you use DevStack, manually reactivate the loopback device with the losetup command. I don't think that your creating a logical volume changed anything.