RMAN恢复NBU磁带库的备份经常报RMAN-10038和RMAN-03002错误

[Samdy_Chan]

各位好：
之前我们在Oracle RAC主库做了NBU全备进磁带的备份，现在将其 restore database 还原数据文件到备库时，经常会报如下的错误：
channel d2: restoring datafile 00178 to /share/mydb/datafile/xxt108.dbf
channel d2: restoring datafile 00260 to /share/mydb/datafile/xxtidx70.dbf
channel d2: restoring datafile 00343 to /share/mydb/datafile/xxtidx83.dbf
channel d2: restoring datafile 00408 to /share/mydb/datafile/xxtidx103.dbf
channel d2: reading from backup piece bk_10932_1_910658292
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 05/06/2016 02:11:16
RMAN-10038: database session for channel d2 terminated unexpectedly

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有时重试多一两次又可以了，但到从别的 backup piece 恢复的时候，又报如上的错误了。请问这是怎么回事？
恢复脚本如下：
$ cat rman_restore.sh
#!/bin/sh


export NLS_LANG="AMERICAN_AMERICA.ZHS16GBK"


rman target / log /home/oracle/myrman.log <<EOF
run {
allocate channel d1 type 'SBT_TAPE';
allocate channel d2 type 'SBT_TAPE';
send channel d1 'NB_ORA_SERV=SCLOUD-GD-NBU,NB_ORA_CLIENT=mydb1,NB_ORA_POLICY=oracle_db_mydb1_full';
send channel d2 'NB_ORA_SERV=SCLOUD-GD-NBU,NB_ORA_CLIENT=mydb1,NB_ORA_POLICY=oracle_db_mydb1_full';
restore database;
release channel d1;
release channel d2;
}
EOF

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环境是，主备机都是 AIX 6.1 操作系统，数据库版本是 11.2.0.4，NBU 服务器版本是 7.6.0.3 for Windows，NBU客户端版本是 7.5 for AIX
麻烦哪位高人帮忙看看，感谢！