asm diskgroup中的Usable_file_MB和Req_mir_free_MB

[root@rhel63single rules.d]# su - grid
[grid@rhel63single ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Fri Sep 18 06:07:37 2015

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Automatic Storage Management option

SQL> 
SQL> 
SQL> 
SQL> set pagesize 200
SQL> set linesize 150
SQL> col path format a20;
SQL> col group_name format a10
SQL> col name format a20
SQL> col FAILGROUP_TYPE format a15
SQL> col FAILGROUP format a15
SQL> select a.group_number,b.name as group_name,a.FAILGROUP,a.FAILGROUP_TYPE,a.name,a.path,a.state,a.total_mb
  2  from v$asm_disk a,v$asm_diskgroup b where a.group_number=b.group_number;

GROUP_NUMBER GROUP_NAME FAILGROUP       FAILGROUP_TYPE  NAME                 PATH                 STATE      TOTAL_MB
------------ ---------- --------------- --------------- -------------------- -------------------- -------- ----------
           1 DATA       DATA_0000       REGULAR         DATA_0000            /dev/raw/raw1        NORMAL         2047
           1 DATA       DATA_0001       REGULAR         DATA_0001            /dev/raw/raw2        NORMAL         2047
           1 DATA       DATA_0000       REGULAR         DATA_0002            /dev/raw/raw3        NORMAL         2047
           1 DATA       DATA_0001       REGULAR         DATA_0003            /dev/raw/raw4        NORMAL         2047

SQL> Set pagesize 100
SQL> Set linesize 200
SQL> Col name format a15
SQL> select GROUP_NUMBER,NAME,STATE,TYPE,TOTAL_MB,FREE_MB,REQUIRED_MIRROR_FREE_MB,USABLE_FILE_MB from v$asm_diskgroup;

GROUP_NUMBER NAME            STATE       TYPE     TOTAL_MB    FREE_MB REQUIRED_MIRROR_FREE_MB USABLE_FILE_MB
------------ --------------- ----------- ------ ---------- ---------- ----------------------- --------------
           1 DATA            MOUNTED     NORMAL       8188       8064                    2047           3008

SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Automatic Storage Management option
[grid@rhel63single ~]$ asmcmd
ASMCMD> lsdg
State    Type    Rebal  Sector  Block       AU  Total_MB  Free_MB  Req_mir_free_MB  Usable_file_MB  Offline_disks  Voting_files  Name
MOUNTED  NORMAL  N         512   4096  1048576      8188     8064             2047            3008              0             N  DATA/