现象：NBU在备份数据库时，脚本分配了4个通道进行数据库备份。0,1，2,3，号channel 进行rman备份，备份过程中会提示通道不可用，切换到其他通道进行备份。此故障无规律，不定期产生此类错误。

错误提示：
NBU端提示错误代码6，：the backup failed to back up the requested files;

rman日志上报错显示：
rman-03009:failure of backup command on ch01 channl at 02/24/2020 17:00:31
ORA-27192:skgfcls:sbtclose2 returned error - failed to close file
ORA-19502:error received form media manager layer,error text:Failed to process backup file <bk_25132_1)1032882570>
ORA-19502:write error on file “bk_25132_1_1032882570”,block number 13301921(block size 8192)
ORA-27030:skggwrt:sbtwrite2 returned error
ORA-19511:Error received from media manager layer ,error text:
VXBSASendData:Failed with error:
channel ch01 disabled,job failed on it will be run on another channel

问题：
1.此问题无法确定是NBU备份问题还是RMAN问题；怎么确认是哪边的问题？
2.rman备份日志上并没有太多关于通道不可用的详细日志。怎么查更加详细的日志？