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该文主要是把当前我所知道的检测Oracle数据文件中在系统上真实数据的起始偏移量的方式，该文档只作为介绍检测偏移量的方式，关于偏移量的相关信息参考《如何计算oracle文件的偏移量》
1.v$datafile视图中的BLOCK1_OFFSET字段可以找出偏移量
默认为8192，在一个块为8k的数据库中每个数据文件在创建时候都会在文件头创建一个OS Header Block，该块大小与数据库块大小一致，所以默认的偏移量都是8192。但是由于现在raw用的少了因为raw中也会为os file system预留空间，在aix为4k，在AIX平台中使用裸设备的文件实际偏移量应该是8192+4096.
SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi PL/SQL Release 10.2.0.5.0 - Production CORE 10.2.0.5.0 Production TNS for IBM/AIX RISC System/6000: Version 10.2.0.5.0 - Productio NLSRTL Version 10.2.0.5.0 - Production SQL> set linesize 200 SQL> col name for a50 SQL> select name,block1_offset from v$datafile NAME BLOCK1_OFFSET -------------------------------------------------- ------------- /data/ludatou/system01.dbf 8192 /data/ludatou/undotbs01.dbf 8192 /data/ludatou/sysaux01.dbf 8192 /data/ludatou/users01.dbf 8192
2.Oracle自带的dbfsize工具
无偏移量情况：
$ dbfsize /dev/rlvsystem01 Database file: /dev/rlvsystem01 Database file type: raw device without 4K starting offset Database file size: 40960 8192 byte blocks
有偏移量情况：
MDDB$dbfsize /dev/rloradb1 Database file: /dev/rloradb1 Database file type: raw device Database file size: 262016 8192 byte blocks
3.AIX系统下使用lslv的命令确认是否存在
#lslv datalv LOGICAL VOLUME: DATALV VOLUME GROUP: datavg LV IDENTIFIER: 00c3dff400004c00000001217a9d839e.84 PERMISSION: read/write VG STATE: active/complete LV STATE: closed/syncd TYPE: raw WRITE VERIFY: off MAX LPs: 1024 PP SIZE: 32 megabyte(s) COPIES: 1 SCHED POLICY: parallel LPs: 64 PPs: 64 STALE PPs: 0 BB POLICY: relocatable INTER-POLICY: maximum RELOCATABLE: yes INTRA-POLICY: middle UPPER BOUND: 1024 MOUNT POINT: N/A LABEL: None MIRROR WRITE CONSISTENCY: on/ACTIVE EACH LP COPY ON A SEPARATE PV ?: yes Serialize IO ?: NO DEVICESUBTYPE : DS_LVZ
当存在DEVICESUBTYPE : DS_LVZ时候证明存在偏移量。
4.在AIX上使用checkoffset脚本检测
使用方法：checkoffset uraw_name
该脚本如下：
#!/bin/ksh # input: # string: raw character device to check # output: # numeric: offset in raw device where oracle data begins # error exit codes: # 255 - usage # 254 - block device (instead of raw device) # 253 - not a raw device (regular file, directory, etc.) # 252 - LV not recognized by 'lslv' command # notes: # This script checks the output of the AIX 'lslv' command for a device subtype of DS_LVZ. # Note that most implementations of 'lslv' will only output the DEVICESUBTYPE field if # the value is something other than DS_LV. If the DEVICESUBTYPE field is not displayed, # or displays a value other than DS_LVZ, then offset is output as 4096, otherwise 0. A # device subtype of DS_LVZ indicates that the normal AIX Logical Volume Control Block # (lvcb) does not occupy the first 512 bytes of the raw device file, and Oracle data # begins at offset 0. A device subtype of DS_LV (default) indicates the first 512 bytes # of the raw device are occupied by the AIX lvcb, and Oracle data begins at offset 4096. # check that one, and only one, parameter was passed if [ $# -lt 1 -o $# -gt 1 ]; then /usr/bin/echo "Usage: checkoffset raw_device" /usr/bin/echo "Example: checkoffset /dev/rASMRAW1" exit 255 fi # resolve relative path to full path dirn=`/usr/bin/dirname $1` if [ $dirn = "." ]; then dirn=`/usr/bin/pwd` fi if [ $dirn = "/" ]; then dirn="" fi basn=`/usr/bin/basename $1` rdev="$dirn/$basn" # check whether the parameter passed is a block device if [ -b $1 ]; then /usr/bin/echo "Error: $rdev is a block device" exit 254 fi # check whether the parameter passed is a raw character device if [ ! -c $1 ]; then /usr/bin/echo "Error: $rdev is not a raw character device" exit 253 fi # strip the 'r' from the device name to get the LV name lvname=`/usr/bin/echo $basn | /usr/bin/cut -c 2-` # check whether lslv accepts the LV name as valid lvchk=`/usr/sbin/lslv $lvname > /dev/null 2>&1 ; print $?` if [ $lvchk != "0" ]; then /usr/bin/echo "Error: Command failed: /usr/sbin/lslv $lvname" /usr/sbin/lslv $lvname exit 252 fi # check lslv output for DEVICESUBTYPE of DS_LVZ and set offset offset=`/usr/sbin/lslv $lvname | /usr/bin/grep DEVICESUBTYPE` offset=`echo $offset | /usr/bin/grep DS_LVZ ; print $?` if [ $offset = "0" ]; then offset="0" else offset="4096" fi # display offset and exit cleanly echo $offset exit 0
