Problem while extending the Fiberchannel Storage domain

Respected Sir

I am having redhat enterprise virtulization manager 3.1.40

and running 3 rhev-h host version 6.3

While add the lun to my  primary fc storage domain getting the following error

Error: Cannot extend Storage Domain. Storage device is unreachable from ${hostName}.

and unable to extend the storage

but when i cross checked the host while going to their running vm and try to add the direct lun it is showing on all

RHEV-h vms

then what is a problem

Please reply asap