[20161028]rman与filesperset=1.txt
--rman备份数据库，我喜欢设置filesperset=1.这样每个备份集仅仅1个数据文件，我个人一直认为这样恢复时会快一些。
--我同事总嫌这样备份文件太多修改为filesperset=4.我通过例子说明我的看法：
1.环境：
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
CREATE TABLESPACE SUGAR DATAFILE
'/mnt/ramdisk/book/sugar01.dbf' SIZE 30M AUTOEXTEND ON NEXT 16M MAXSIZE UNLIMITED
NOLOGGING
ONLINE
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO
FLASHBACK ON;
CREATE TABLESPACE TEA DATAFILE
'/mnt/ramdisk/book/tea01.dbf' SIZE 30M AUTOEXTEND ON NEXT 16M MAXSIZE UNLIMITED
NOLOGGING
ONLINE
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO
FLASHBACK ON;
SCOTT@book> create table t1 tablespace sugar as select rownum id ,lpad('A',32,'A') name from dual connect by level<=2e5;
Table created.
SCOTT@book> create table t2 tablespace tea as select rownum id ,lpad('B',32,'B') name from dual connect by level<=2e5;
Table created.
SCOTT@book> alter system checkpoint ;
System altered.
--//分别建立2个表在不同的表空间。内容1个是AAAA...，另外一个是BBBB..。
2.备份测试：
RMAN> report schema ;
using target database control file instead of recovery catalog
Report of database schema for database with db_unique_name BOOK
List of Permanent Datafiles
===========================
File Size(MB) Tablespace RB segs Datafile Name
---- -------- -------------------- ------- ------------------------
1 750 SYSTEM *** /mnt/ramdisk/book/system01.dbf
2 760 SYSAUX *** /mnt/ramdisk/book/sysaux01.dbf
3 85 UNDOTBS1 *** /mnt/ramdisk/book/undotbs01.dbf
4 50 USERS *** /mnt/ramdisk/book/users01.dbf
5 313 EXAMPLE *** /mnt/ramdisk/book/example01.dbf
6 30 SUGAR *** /mnt/ramdisk/book/sugar01.dbf
7 30 TEA *** /mnt/ramdisk/book/tea01.dbf
List of Temporary Files
=======================
File Size(MB) Tablespace Maxsize(MB) Tempfile Name
---- -------- -------------------- ----------- --------------------
1 29 TEMP 32767 /mnt/ramdisk/book/temp01.dbf
RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters are successfully stored
--//仅仅打开1个并行。这样测试可以实现备份在一个备份集中。
RMAN> backup datafile 6,7 format '/u01/backup/datafile6_7_%U' ;
Starting backup at 2016-10-28 09:13:33
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00006 name=/mnt/ramdisk/book/sugar01.dbf
input datafile file number=00007 name=/mnt/ramdisk/book/tea01.dbf
channel ORA_DISK_1: starting piece 1 at 2016-10-28 09:13:33
channel ORA_DISK_1: finished piece 1 at 2016-10-28 09:13:34
piece handle=/u01/backup/datafile6_7_0crjft5t_1_1 tag=TAG20161028T091333 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 2016-10-28 09:13:34
--检查备份：
$ strings /u01/backup/datafile6_7_0crjft5t_1_1 | less
...
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
d AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
cd AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
cc AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
cb AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
ca AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
c` AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
c_ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
c^ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
c] AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
c\ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
d <
K BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
J BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
I BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
H BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
G BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
...
ca BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
c` BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
c_ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
c^ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
c] BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
c\ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
g >
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,
--你可以发现AAAA，BBBB字符串出现的顺序是交替进行的，也就是rman备份是2个文件同时读取写入备份集，而不是先备份数据文件6，再备
--份数据文件7.
3.这样在恢复整个数据库估计问题不大。
--实际上如果你IO不好，估计恢复也很慢，假设选择filesperset=4,如果又打开并行，这样同时写入的数据文件数量会很多。当然这仅仅是
--我的猜测.
但是如果你恢复时如果仅仅恢复数据文件6，读取备份集的量就是整个备份集，这样恢复相对就慢了。
--//恢复1个数据文件看看。
SCOTT@book> alter tablespace sugar offline ;
Tablespace altered.
$ strace -f -o /tmp/aa.txt rman target /
Recovery Manager: Release 11.2.0.4.0 - Production on Fri Oct 28 09:30:28 2016
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
connected to target database: BOOK (DBID=1337401710)
RMAN> restore tablespace sugar ;
Starting restore at 2016-10-28 09:30:47
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=56 device type=DISK
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00006 to /mnt/ramdisk/book/sugar01.dbf
channel ORA_DISK_1: reading from backup piece /u01/backup/datafile6_7_0crjft5t_1_1
channel ORA_DISK_1: piece handle=/u01/backup/datafile6_7_0crjft5t_1_1 tag=TAG20161028T091333
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
Finished restore at 2016-10-28 09:30:50
RMAN> quit
Recovery Manager complete.
$ ls -l /u01/backup/datafile6_7_0crjft5t_1_1
-rw-r----- 1 oracle oinstall 22118400 2016-10-28 09:13:33 /u01/backup/datafile6_7_0crjft5t_1_1
--注意文件大小22118400。
$ egrep 'pread\(258,|pwrite\(259,' /tmp/aa.txt >| /tmp/a2.txt
47653 pread(258, "\v\242\0\0\1\0\200\1\0\0\0\0\0\0\1\4\34b\0\0\0\0\0\0\0\4 \vn!\267O"..., 8192, 8192) = 8192
47656 pread(258, "\23\242\0\0\1\0\0\0\307\247#\0\0\0\1\4\200Z\0\0\0\4 \v\0\4 \vn!\267O"..., 1040384, 8192) = 1040384
47656 pread(258, "\36\242\0\0\200\0\200\1\26\242#\0\0\0\1\4\5B\1\0\6\0\0\0\200\0\301\3\0\0\0\0"..., 1048576, 1048576) = 1048576
47656 pread(258, "!\242\0\0\200\0\200\1\202\246#\0\0\0\32\4B\335\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 2097152) = 1048576
47656 pread(258, "!\242\0\0\200\0\300\1\310\246#\0\0\0\32\4~\335\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 3145728) = 1048576
47656 pread(258, " \242\0\0\200\1\200\1\202\246#\0\0\0\2\4\326\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 4194304) = 1048576
47656 pwrite(259, "\0\242\0\0\1\0\200\1\0\0\0\0\0\0\1\5\201\246\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1040384, 8192) = 1040384
47656 pread(258, " \242\0\0\200\1\300\1\310\246#\0\0\0\2\4-\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 5242880) = 1048576
47656 pwrite(259, " \242\0\0\200\0\200\1\202\246#\0\0\0\4\4]\362\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 1048576) = 1048576
47656 pread(258, " \242\0\0\200\1\200\1\202\246#\0\0\0\2\4\324\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 6291456) = 1048576
47656 pread(258, " \242\0\0\200\1\300\1\310\246#\0\0\0\2\4/\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 7340032) = 1048576
47656 pwrite(259, " \242\0\0\0\1\200\1\202\246#\0\0\0\2\4\27\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 2097152) = 1048576
47656 pread(258, " \242\0\0\200\2\200\1\202\246#\0\0\0\2\4\322\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 8388608) = 1048576
47656 pread(258, " \242\0\0\200\2\300\1\310\246#\0\0\0\2\4)\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 9437184) = 1048576
47656 pwrite(259, " \242\0\0\200\1\200\1\202\246#\0\0\0\2\4\25\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 3145728) = 1048576
47656 pread(258, " \242\0\0\200\2\200\1\202\246#\0\0\0\2\4\320\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 10485760) = 1048576
47656 pread(258, " \242\0\0\200\2\300\1\310\246#\0\0\0\2\4+\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 11534336) = 1048576
47656 pwrite(259, " \242\0\0\0\2\200\1\202\246#\0\0\0\2\4\23\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 4194304) = 1048576
47656 pread(258, " \242\0\0\200\3\200\1\202\246#\0\0\0\2\4\316\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 12582912) = 1048576
47656 pread(258, " \242\0\0\200\3\300\1\310\246#\0\0\0\2\0045\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 13631488) = 1048576
47656 pwrite(259, " \242\0\0\200\2\200\1\202\246#\0\0\0\2\4\21\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 5242880) = 1048576
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
47656 pread(258, " \242\0\0\200\3\200\1\202\246#\0\0\0\2\4\314\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 14680064) = 1048576
47656 pread(258, " \242\0\0\200\3\300\1\310\246#\0\0\0\2\0047\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 15728640) = 1048576
47656 pwrite(259, " \242\0\0\0\3\200\1\202\246#\0\0\0\2\4\17\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 6291456) = 1048576
47656 pread(258, " \242\0\0\200\4\200\1\202\246#\0\0\0\2\4\312\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 16777216) = 1048576
47656 pread(258, " \242\0\0\200\4\300\1\310\246#\0\0\0\2\0041\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 17825792) = 1048576
47656 pwrite(259, " \242\0\0\200\3\200\1\202\246#\0\0\0\2\4\r\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 7340032) = 1048576
47656 pread(258, " \242\0\0\200\4\200\1\202\246#\0\0\0\2\4\310\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 18874368) = 1048576
47656 pread(258, " \242\0\0\200\4\300\1\310\246#\0\0\0\2\0043\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 19922944) = 1048576
47656 pwrite(259, " \242\0\0\0\4\200\1\202\246#\0\0\0\2\4\v\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 8388608) = 1048576
47656 pread(258, " \242\0\0\200\5\200\1\202\246#\0\0\0\3\4i\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 20971520) = 1048576
47656 pread(258, "\6\242\0\0\200\5\300\1\300\247#\0\0\0\1\6\223\213\2\0\1\0\0\0\340Z\1\0\225\246#\0"..., 98304, 22020096) = 98304
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
47656 pwrite(259, " \242\0\0\200\4\200\1\202\246#\0\0\0\2\4\t\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 9437184) = 1048576
47656 pwrite(259, " \242\0\0\0\5\200\1\202\246#\0\0\0\2\4\7\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 10485760) = 1048576
47656 pwrite(259, ":\242\0\0\200\5\200\1\10 \16\0\0\0\1\0044\230\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 11534336) = 1048576
47656 pwrite(259, ":\242\0\0\0\6\200\1\10 \16\0\0\0\1\4\264\233\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 12582912) = 1048576
47656 pwrite(259, ":\242\0\0\200\6\200\1\10 \16\0\0\0\1\0044\233\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 13631488) = 1048576
47656 pwrite(259, ":\242\0\0\0\7\200\1\10 \16\0\0\0\1\4\264\232\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 14680064) = 1048576
47656 pwrite(259, ":\242\0\0\200\7\200\1\10 \16\0\0\0\1\0044\232\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 15728640) = 1048576
47656 pwrite(259, ":\242\0\0\0\10\200\1\10 \16\0\0\0\1\4\264\225\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 16777216) = 1048576
47656 pwrite(259, ":\242\0\0\200\10\200\1\10 \16\0\0\0\1\0044\225\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 17825792) = 1048576
47656 pwrite(259, ":\242\0\0\0\t\200\1\10 \16\0\0\0\1\4\264\224\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 18874368) = 1048576
47656 pwrite(259, ":\242\0\0\200\t\200\1\10 \16\0\0\0\1\0044\224\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 19922944) = 1048576
47656 pwrite(259, ":\242\0\0\0\n\200\1\10 \16\0\0\0\1\4\264\227\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 20971520) = 1048576
47656 pwrite(259, ":\242\0\0\200\n\200\1\10 \16\0\0\0\1\0044\227\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 22020096) = 1048576
47656 pwrite(259, ":\242\0\0\0\v\200\1\10 \16\0\0\0\1\4\264\226\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 23068672) = 1048576
47656 pwrite(259, ":\242\0\0\200\v\200\1\10 \16\0\0\0\1\0044\226\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 24117248) = 1048576
47656 pwrite(259, ":\242\0\0\0\f\200\1\10 \16\0\0\0\1\4\264\221\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 25165824) = 1048576
47656 pwrite(259, ":\242\0\0\200\f\200\1\10 \16\0\0\0\1\0044\221\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 26214400) = 1048576
47656 pwrite(259, ":\242\0\0\0\r\200\1\10 \16\0\0\0\1\4\264\220\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 27262976) = 1048576
47656 pwrite(259, ":\242\0\0\200\r\200\1\10 \16\0\0\0\1\0044\220\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 28311552) = 1048576
47656 pwrite(259, ":\242\0\0\0\16\200\1\10 \16\0\0\0\1\4\264\223\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 29360128) = 1048576
47656 pwrite(259, ":\242\0\0\200\16\200\1\10 \16\0\0\0\1\0044\223\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 30408704) = 1048576
47656 pwrite(259, "\0\242\0\0\0\17\200\1\0\0\0\0\0\0\1\5\200\251\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 8192, 31457280) = 8192
47656 pwrite(259, "\v\242\0\0\1\0\200\1\0\0\0\0\0\0\1\4I\240\0\0\0\0\0\0\0\4 \vn!\267O"..., 8192, 8192) = 8192
--注意看~部分，说明读取这个备份文件到22020096偏移，后面为什么有这么多写，实际上我备份的数据文件大小30M，但是仅仅前面的
--10M有数据，所以后面仅仅写空块。
47656 pwrite(259, " \242\0\0\0\5\200\1\202\246#\0\0\0\2\4\7\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 10485760) = 1048576
--10485760/8192=1280
BBED> set dba 6,1280
DBA 0x01800500 (25167104 6,1280)
BBED> dump /v count 100
File: /mnt/ramdisk/book/sugar01.dbf (6)
Block: 1280 Offsets: 0 to 99 Dba:0x01800500
-----------------------------------------------------------------------------------------------------------
20a20000 00058001 82a62300 00000204 07f30000 00000000 00000000 00000000 l .........#.....................
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 l ................................
00000000 00000000 00000000 04000000 ffffffff 00000000 02000000 40000000 l ............................@...
01000100 l ....
<32 bytes per line>
--pwrite 里面的是8进制。
--20 (八进制)=2*8=16 = 0x10
--242(八进制)=2*8*8+4*8+2=162 = 0xa2
--200(八进制)=2*8*8 = 128 = 0x80
--大家可以自行测试，可以对上的。
--如果你再仔细看可以发现执行2次pread 每次1M，写1次pwrite每次1M。也就是存在无用的读取操作，我取其中一段来分析：
47656 pread(258, " \242\0\0\200\3\200\1\202\246#\0\0\0\2\4\314\363\1\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 14680064) = 1048576
47656 pread(258, " \242\0\0\200\3\300\1\310\246#\0\0\0\2\0047\376\2\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 15728640) = 1048576
47656 pwrite(259, " \242\0\0\0\3\200\1\202\246#\0\0\0\2\4\17\363\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 6291456) = 1048576
--你可以发现写入内容在第一个pread的开头并一样。也就是这样恢复读取了数据文件7(也就是表空间tea的备份信息).
4.可以发现这样在仅仅恢复1个数据文件的情况下，要扫描整个备份集。
$ grep pread /tmp/a2.txt | cut -f2 -d= |xargs echo | sed 's/ /+/g' | bc -l
22118400
$ ls -l /u01/backup/datafile6_7_0crjft5t_1_1
-rw-r----- 1 oracle oinstall 22118400 2016-10-28 09:13:33 /u01/backup/datafile6_7_0crjft5t_1_1
--注意文件大小22118400。这样读取的数量一致。
5.而如果使用参数filesperset=1,这样每个备份集仅仅1个文件就没有这个问题了。
RMAN> recover tablespace sugar ;
Starting recover at 2016-10-28 10:36:31
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:00
Finished recover at 2016-10-28 10:36:31
SCOTT@book> alter tablespace sugar online ;
Tablespace altered.
RMAN> backup datafile 6,7 filesperset=1 format '/u01/backup/datafile6_7_%U' ;
Starting backup at 2016-10-28 10:39:03
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00006 name=/mnt/ramdisk/book/sugar01.dbf
channel ORA_DISK_1: starting piece 1 at 2016-10-28 10:39:03
channel ORA_DISK_1: finished piece 1 at 2016-10-28 10:39:04
piece handle=/u01/backup/datafile6_7_0drjg267_1_1 tag=TAG20161028T103903 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00007 name=/mnt/ramdisk/book/tea01.dbf
channel ORA_DISK_1: starting piece 1 at 2016-10-28 10:39:05
channel ORA_DISK_1: finished piece 1 at 2016-10-28 10:39:06
piece handle=/u01/backup/datafile6_7_0erjg269_1_1 tag=TAG20161028T103903 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 2016-10-28 10:39:06
$ ls -l /u01/backup/datafile6_7_0*
-rw-r----- 1 oracle oinstall 22118400 2016-10-28 09:13:33 /u01/backup/datafile6_7_0crjft5t_1_1
-rw-r----- 1 oracle oinstall 11075584 2016-10-28 10:39:03 /u01/backup/datafile6_7_0drjg267_1_1
-rw-r----- 1 oracle oinstall 11075584 2016-10-28 10:39:05 /u01/backup/datafile6_7_0erjg269_1_1
--这样每个备份集1个数据文件，就可以避免这个问题了。
RMAN> list backup of datafile 6,7;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
5 Full 21.09M DISK 00:00:00 2016-10-28 09:13:33
BP Key: 5 Status: AVAILABLE Compressed: NO Tag: TAG20161028T091333
Piece Name: /u01/backup/datafile6_7_0crjft5t_1_1
List of Datafiles in backup set 5
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- ------------------- ----
6 Full 2336756 2016-10-28 09:13:33 /mnt/ramdisk/book/sugar01.dbf
7 Full 2336756 2016-10-28 09:13:33 /mnt/ramdisk/book/tea01.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
6 Full 10.55M DISK 00:00:00 2016-10-28 10:39:03
BP Key: 6 Status: AVAILABLE Compressed: NO Tag: TAG20161028T103903
Piece Name: /u01/backup/datafile6_7_0drjg267_1_1
List of Datafiles in backup set 6
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- ------------------- ----
6 Full 2341184 2016-10-28 10:39:03 /mnt/ramdisk/book/sugar01.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
7 Full 10.55M DISK 00:00:00 2016-10-28 10:39:05
BP Key: 7 Status: AVAILABLE Compressed: NO Tag: TAG20161028T103903
Piece Name: /u01/backup/datafile6_7_0erjg269_1_1
List of Datafiles in backup set 7
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- ------------------- ----
7 Full 2341185 2016-10-28 10:39:05 /mnt/ramdisk/book/tea01.dbf
--总结：
备份的目的总是要利于恢复的，建议使用参数filesperset =1 ,这样虽然数据文件很多时，备份的文件也很多，但是这样更加利于恢复。
