Backup archivelog not backed up 2 times

1.Backup the archivelog all not backed up 2 times;
RMAN> run
2> {
3> backup
4> as backupset
5> tag="archivelog_backup"
6> archivelog all
7> not backed up 2 times;
8> }

Starting backup at 15-MAY-2014 07:42:19
current log archived
using channel ORA_DISK_1
using channel ORA_DISK_2
using channel ORA_DISK_3
using channel ORA_DISK_4
using channel ORA_DISK_5
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=1 RECID=19 STAMP=847442778
input archived log thread=1 sequence=2 RECID=20 STAMP=847518670
input archived log thread=1 sequence=3 RECID=21 STAMP=847518671
input archived log thread=1 sequence=4 RECID=22 STAMP=847518681
channel ORA_DISK_1: starting piece 1 at 15-MAY-2014 07:42:23
channel ORA_DISK_2: starting archived log backup set
channel ORA_DISK_2: specifying archived log(s) in backup set
input archived log thread=1 sequence=5 RECID=23 STAMP=847527192
input archived log thread=1 sequence=6 RECID=34 STAMP=847534249
input archived log thread=1 sequence=7 RECID=32 STAMP=847534249
input archived log thread=1 sequence=8 RECID=33 STAMP=847534249
channel ORA_DISK_2: starting piece 1 at 15-MAY-2014 07:42:24
channel ORA_DISK_3: starting archived log backup set
channel ORA_DISK_3: specifying archived log(s) in backup set
input archived log thread=1 sequence=1 RECID=35 STAMP=847534456
input archived log thread=1 sequence=2 RECID=37 STAMP=847534546
input archived log thread=1 sequence=3 RECID=38 STAMP=847589637
channel ORA_DISK_3: starting piece 1 at 15-MAY-2014 07:42:24
channel ORA_DISK_4: starting archived log backup set
channel ORA_DISK_4: specifying archived log(s) in backup set
input archived log thread=1 sequence=4 RECID=39 STAMP=847589868
input archived log thread=1 sequence=5 RECID=40 STAMP=847590813
input archived log thread=1 sequence=6 RECID=41 STAMP=847591156
input archived log thread=1 sequence=7 RECID=42 STAMP=847607429
channel ORA_DISK_4: starting piece 1 at 15-MAY-2014 07:42:25
channel ORA_DISK_5: starting archived log backup set
channel ORA_DISK_5: specifying archived log(s) in backup set
input archived log thread=1 sequence=8 RECID=43 STAMP=847608984
input archived log thread=1 sequence=9 RECID=44 STAMP=847609149
input archived log thread=1 sequence=10 RECID=45 STAMP=847609270
input archived log thread=1 sequence=11 RECID=46 STAMP=847611739
channel ORA_DISK_5: starting piece 1 at 15-MAY-2014 07:42:32
channel ORA_DISK_1: finished piece 1 at 15-MAY-2014 07:42:32
piece handle=+DATA/cvrman/backupset/2014_05_15/annnf0_archivelog_backup_0.305.847611743 tag=ARCHIVELOG_BACKUP comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:09
channel ORA_DISK_2: finished piece 1 at 15-MAY-2014 07:42:32
piece handle=+DATA/cvrman/backupset/2014_05_15/annnf0_archivelog_backup_0.282.847611751 tag=ARCHIVELOG_BACKUP comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:08
channel ORA_DISK_3: finished piece 1 at 15-MAY-2014 07:42:32
piece handle=+DATA/cvrman/backupset/2014_05_15/annnf0_archivelog_backup_0.291.847611745 tag=ARCHIVELOG_BACKUP comment=NONE
channel ORA_DISK_3: backup set complete, elapsed time: 00:00:08
channel ORA_DISK_4: finished piece 1 at 15-MAY-2014 07:42:32
piece handle=+DATA/cvrman/backupset/2014_05_15/annnf0_archivelog_backup_0.286.847611745 tag=ARCHIVELOG_BACKUP comment=NONE
channel ORA_DISK_4: backup set complete, elapsed time: 00:00:07
channel ORA_DISK_5: finished piece 1 at 15-MAY-2014 07:42:33
piece handle=+DATA/cvrman/backupset/2014_05_15/annnf0_archivelog_backup_0.280.847611753 tag=ARCHIVELOG_BACKUP comment=NONE
channel ORA_DISK_5: backup set complete, elapsed time: 00:00:01
Finished backup at 15-MAY-2014 07:42:33

Starting Control File and SPFILE Autobackup at 15-MAY-2014 07:42:34
piece handle=+DATA/cvrman/autobackup/2014_05_15/s_847611754.276.847611755 comment=NONE
Finished Control File and SPFILE Autobackup at 15-MAY-2014 07:42:37