in extreme BD 8806, io can see only one MSM, only MSM B is showing master..s there any specific reason
As AlexandrP said, you can have 2 MSM at the same time in a BD8806. It's recommended to have 2 MSM for obvious redundancy consideration, and also for highest throughput. MSMs are working in a load-sharing mode for their fabric role, meaning each MSM provide half the bandwidth to the chassis. They work as Master/Backup for the Management.
Am I understanding you do have a msm in slot A but is shows empty?? If so then it may be faulty or worse a different model... If you do have one there I would hook a console cable up to it schedule a maintenance window and unseat it for a couple of minutes and reseat it.. watch the boot us process from console session .... if it is empty then you really should have a second one in there as other have said you are not allowing the 8806 to run at top performance. After reading the guide about syncing and dealing with the two msm's shout back if additional questions pop up...