# File lib/fog/compute/requests/aws/create_volume.rb, line 40
        def create_volume(availability_zone, size, snapshot_id = nil)
          response = Excon::Response.new
          if availability_zone && (size || snapshot_id)
            snapshot = self.data[:snapshots][snapshot_id]
            if snapshot_id && !snapshot
              raise Fog::Compute::AWS::NotFound.new("The snapshot '#{snapshot_id}' does not exist.")
            end

            if snapshot && size && size != snapshot['volumeSize']
              raise Fog::Compute::AWS::NotFound.new("The snapshot '#{snapshot_id}' with the specified size of '#{size}' does not exist.")
            elsif snapshot && !size
              size = snapshot['volumeSize']
            end

            response.status = 200
            volume_id = Fog::AWS::Mock.volume_id
            data = {
              'availabilityZone'  => availability_zone,
              'attachmentSet'     => [],
              'createTime'        => Time.now,
              'size'              => size,
              'snapshotId'        => snapshot_id,
              'status'            => 'creating',
              'tagSet'            => {},
              'volumeId'          => volume_id
            }
            self.data[:volumes][volume_id] = data
            response.body = {
              'requestId' => Fog::AWS::Mock.request_id
            }.merge!(data.reject {|key,value| !['availabilityZone','createTime','size','snapshotId','status','volumeId'].include?(key) })
          else
            response.status = 400
            response.body = {
              'Code' => 'MissingParameter'
            }
            unless availability_zone
              response.body['Message'] = 'The request must contain the parameter availability_zone'
            else
              response.body['Message'] = 'The request must contain the parameter size'
            end
          end
          response
        end