为data磁盘组删除当中一个盘（asm external data盘组中有两块盘）

删除磁盘，注意，假设删掉磁盘之后。数据在剩余磁盘中。是否有足够空间存储。假设空间不够。删除工作不会成功。


检查空间够不够：
select a.GROUP_NUMBER,a.DISK_NUMBER,a.NAME ,decode(sign(a.FREE_MB-d.COLD_USED_MB/ 2),1 ,'Y',- 1,'N' ,'N') from v$asm_diskgroup d,v$asm_disk a where a.GROUP_NUMBER = d.GROUP_NUMBER and a.GROUP_NUMBER = 2;  --自己写的语句，假设推断有问题，请一定告知我。谢谢

1.检查磁盘
GROUP_NUMBER GROUP_NAME NAME                 PATH                 STATE      TOTAL_MB
------------ ---------- -------------------- -------------------- -------- ----------
           0 DATA       DATA2                /dev/raw/raw6        NORMAL         8192
           5 FRA        FRA                  /dev/raw/raw5        NORMAL         8192
           0 DATA       DATA                 /dev/raw/raw4        NORMAL         8192
           0 CRS        CRS_0002             /dev/raw/raw3        NORMAL         3072
           0 CRS        CRS_0001             /dev/raw/raw2        NORMAL         3072
           0 CRS        CRS_0000             /dev/raw/raw1        NORMAL         3072

2.删除
SQL> alter diskgroup data drop disk data2;

Diskgroup altered.

GROUP_NUMBER GROUP_NAME NAME                 PATH                 STATE      TOTAL_MB
------------ ---------- -------------------- -------------------- -------- ----------
           0 DATA       DATA2                /dev/raw/raw6        DROPPING       8192
           5 FRA        FRA                  /dev/raw/raw5        NORMAL         8192
           0 DATA       DATA                 /dev/raw/raw4        NORMAL         8192
           0 CRS        CRS_0002             /dev/raw/raw3        NORMAL         3072
           0 CRS        CRS_0001             /dev/raw/raw2        NORMAL         3072
           0 CRS        CRS_0000             /dev/raw/raw1        NORMAL         3072

3.等了一会

GROUP_NUMBER GROUP_NAME NAME                 PATH                 STATE      TOTAL_MB
------------ ---------- -------------------- -------------------- -------- ----------
           5 FRA        FRA                  /dev/raw/raw5        NORMAL         8192
           0 DATA       DATA                 /dev/raw/raw4        NORMAL         8192
           0 CRS        CRS_0002             /dev/raw/raw3        NORMAL         3072
           0 CRS        CRS_0001             /dev/raw/raw2        NORMAL         3072
           0 CRS        CRS_0000             /dev/raw/raw1        NORMAL         3072

注：假设在dropping状态中。忽然反悔了，那么
alter diskgroup data undrop disks;
假设删完了，那就add吧。