[20161110]数据文件的第0块.txt

--如果数据文件的第0块是OS块信息，以前的测试如果rman做备份集都不会备份。
--如果这块损坏，里面讲问题不大，你甚至可以不修复，当然重建控制文件就出现问题。

--而且解决也很简单，就是建立一样大小的数据文件，然后copy回去。做一个测试例子：

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 40M AUTOEXTEND ON NEXT 16M MAXSIZE UNLIMITED
LOGGING
ONLINE
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO
FLASHBACK ON;

create table t1 tablespace sugar as select rownum id ,lpad('A',32,'A') name from dual connect by level<=1e5;
alter system checkpoint;

2.看看第0块内容，注意实际上建立的数据文件大小是40M+8K。

$ bvi -b 0 -s 8192 /mnt/ramdisk/book/sugar01.dbf
00000000  00 A2 00 00 00 00 C0 FF 00 00 00 00 00 00 00 00 ................
00000010  66 EE 00 00 00 20 00 00 00 14 00 00 7D 7C 7B 7A f.... ......}|{z
00000020  A0 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000030  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000040  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000050  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
...
00001FF0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00002000
}

SCOTT@book> alter tablespace sugar offline ;
Tablespace altered.

--安全期间做1个备份。
$ cp /mnt/ramdisk/book/sugar01.dbf /u01/backup/sugar01.dbf_20161110

--全部清零。
SCOTT@book> alter tablespace sugar online ;
alter tablespace sugar online
*
ERROR at line 1:
ORA-01157: cannot identify/lock data file 6 - see DBWR trace file
ORA-01110: data file 6: '/mnt/ramdisk/book/sugar01.dbf'

--实际上如果在线resize会重写第0块OS块。

3.建立一样大小的数据文件。

CREATE TABLESPACE TEA DATAFILE
  '/mnt/ramdisk/book/tea01.dbf' SIZE 40M AUTOEXTEND ON NEXT 16M MAXSIZE UNLIMITED
LOGGING
ONLINE
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO
FLASHBACK ON;

BBED> info
File#  Name                             Size(blks)
-----  ----                             ----------
     1  /mnt/ramdisk/book/system01.dbf            0
     2  /mnt/ramdisk/book/sysaux01.dbf            0
     3  /mnt/ramdisk/book/undotbs01.dbf           0
     4  /mnt/ramdisk/book/users01.dbf             0
     5  /mnt/ramdisk/book/example01.dbf           0
     6  /mnt/ramdisk/book/sugar01.dbf             0
     7  /mnt/ramdisk/book/tea01.dbf               0

--注意不能这样执行，这个不属于dba地址。
BBED> set dba 7,0
BBED-00205: illegal or out of range DBA (File 7, Block 0)

BBED> help copy
COPY [ DBA | FILE | FILENAME | BLOCK ] TO [ DBA | FILE | FILENAME | BLOCK ]

BBED> copy file 7 block 0 to file 6 block 0
BBED-00309: out of range block number (0)

--问题在于清0后，无法访问
BBED> set file 6 block 0
        FILE#           6
BBED-00309: out of range block number (0)

BBED> dump /v file 7 block 0  count 128 offset 0
File: /mnt/ramdisk/book/tea01.dbf (7)
Block: 0                                 Offsets:    0 to  127                            Dba:0x01c00000
-----------------------------------------------------------------------------------------------------------
00a20000 0000c0ff 00000000 00000000 66ee0000 00200000 00140000 7d7c7b7a l ................f.... ......}|{z
a0810000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 l ................................
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 l ................................
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 l ................................
<32 bytes per line>
}

--直接编辑数据文件6就ok了。

$ bvi -b 0 -s 8192 /mnt/ramdisk/book/sugar01.dbf

:set cm=32

SCOTT@book> alter tablespace sugar online ;
Tablespace altered.

SCOTT@book> select count(*) from t1;
    COUNT(*)
------------
      100000