RMAN备份时提示Fractured block found

在rman备份期间，AIX系统上oracle 10.2.0.3的alertlog出现如下信息：

Tue Jun  7 01:41:58 2011

Hex dump of (file 5, block 938791) in trace file /oracle/product/10.2.0/admin/MS/udump/ms_ora_471880.trc

Corrupt block relative dba: 0x014e5327 (file 5, block 938791)

Fractured block found during backing up datafile

Data in bad block:

 type: 6 format: 2 rdba: 0x014e5327

 last change scn: 0x0007.4e6f12b3 seq: 0x1 flg: 0x06

 spare1: 0x0 spare2: 0x0 spare3: 0x0

 consistency value in tail: 0x14cc0601

 check value in block header: 0xd94b

 computed block checksum: 0x67f

Reread of blocknum=938791, file=/dev/vx/rdsk/oradgMS/lv_ms_Profiles1. found valid data

从日志中可以看到，提示Corrupt的block对应的dba为0x014e5327 (file 5, block 938791)，data block的类型为6（6为trans data，所有的data和index blocks都是该类型）。Oracle发现block有可能corrupt后，进行了reread，结果为found valid data，说明数据块未损坏。

       我们来看一下块断裂的说明：

A Fractured block means that the block is incomplete. Information from the block header does not match the block tail.

原因：

RMAN backups of datafile are being performed while the datafile is involved in heavy I/O.

RMAN reads Oracle blocks from disk. If it finds that the block is fractured,which means it is being actively used, it performs a reread of the block. If that fails again then the block is assumed to be corrupt.

Fractured block found，表示rman发现这个数据块正在被使用，这时rman会进行重新读取，如果再次失败，才认为是坏块。如果第二次尝试读取时成功，则表示数据完好，不会产生影响。

此类信息在IO负载较高的情况下进行rman备份时比较容易出现。

给出的解决方案：

Run the backups when the tablespace has less I/O activity.

建议在空闲时段进行rman备份，以避免出现这类信息。

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