That was a question I got during my present Oracle 11gR2 RAC accelerated course in Duesseldorf: What happens if we drop an ASM Disk that contains a Voting Disk? My answer was: “I suppose that is not allowed” but my motto is “Don’t believe it, test it!” and that is what I did. That is actually one of the good things about doing a course at Oracle University: We can just check out things without affecting critical production systems here in our course environment:

[grid@host01 ~]$ crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   48d3710843274f88bf1eb9b3b5129a7d (ORCL:ASMDISK01) [DATA]
 2. ONLINE   354cfa8376364fd2bfaa1921534fe23b (ORCL:ASMDISK02) [DATA]
 3. ONLINE   762ad94a98554fdcbf4ba5130ac0384c (ORCL:ASMDISK03) [DATA]
Located 3 voting disk(s).

We are on 11.2.0.1 here. The Voting Disk being part of an ASM Diskgroup was an 11gR2 New Feature that I introduced in this posting already. Now let’s try to drop ASMDISK01:

[grid@host01 ~]$ sqlplus / as sysasm

SQL*Plus: Release 11.2.0.1.0 Production on Wed Jun 13 17:18:21 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Real Application Clusters and Automatic Storage Management options

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

SQL> select name,group_number from v$asm_diskgroup;

NAME                           GROUP_NUMBER
------------------------------ ------------
DATA                                      1
ACFS                                      2
FRA                                       3

SQL> select name from v$asm_disk where group_number=1;

NAME
------------------------------
ASMDISK01
ASMDISK02
ASMDISK03
ASMDISK04

SQL> alter diskgroup data drop disk 'ASMDISK01';

Diskgroup altered.

It just did it without error message! We look further:

SQL> select name from v$asm_disk where group_number=1;

NAME
------------------------------
ASMDISK02
ASMDISK03
ASMDISK04

SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Real Application Clusters and Automatic Storage Management options
[grid@host01 ~]$ crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   354cfa8376364fd2bfaa1921534fe23b (ORCL:ASMDISK02) [DATA]
 2. ONLINE   762ad94a98554fdcbf4ba5130ac0384c (ORCL:ASMDISK03) [DATA]
 3. ONLINE   3f0bf16b6eb64f3cbf440a3c2f0da2fd (ORCL:ASMDISK04) [DATA]
Located 3 voting disk(s).

It just moved the Voting Disk silently to another ASM Disk of that Diskgroup.  When I try to drop another ASM Disk from that Diskgroup, the command seems to be silently ignored, because 3 ASM Disks are required here to keep the 3 Voting Disks. Similar behavior with External Redundancy:

[grid@host01 ~]$ 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  EXTERN  N         512   4096  1048576      9788     9645                0            9645              0             N  ACFS/
MOUNTED  NORMAL  N         512   4096  1048576      7341     6431              438            2996              0             N  DATA/
MOUNTED  EXTERN  N         512   4096  1048576      4894     4755                0            4755              0             N  FRA/

I will move the Voting Disk to the FRA Diskgroup. It is a bug of 11.2.0.1 that the Voting_files flag is not Y for the DATA Diskgroup here, by the way.

[grid@host01 ~]$ sudo crsctl replace votedisk +FRA
Successful addition of voting disk 4d586fbecf664f8abf01d272a354fa67.
Successful deletion of voting disk 354cfa8376364fd2bfaa1921534fe23b.
Successful deletion of voting disk 762ad94a98554fdcbf4ba5130ac0384c.
Successful deletion of voting disk 3f0bf16b6eb64f3cbf440a3c2f0da2fd.
Successfully replaced voting disk group with +FRA.
CRS-4266: Voting file(s) successfully replaced
[grid@host01 ~]$ crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   4d586fbecf664f8abf01d272a354fa67 (ORCL:ASMDISK10) [FRA]
Located 1 voting disk(s).
[grid@host01 ~]$ sqlplus / as sysasm

SQL*Plus: Release 11.2.0.1.0 Production on Wed Jun 13 17:36:06 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Real Application Clusters and Automatic Storage Management options

SQL> alter diskgroup fra drop disk 'ASMDISK10';

Diskgroup altered.

SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Real Application Clusters and Automatic Storage Management options
[grid@host01 ~]$ crsctl query css votedisk
##  STATE    File Universal Id                File Name Disk group
--  -----    -----------------                --------- ---------
 1. ONLINE   0b051cf6e6a14ff1bf31ef7bc66098e0 (ORCL:ASMDISK11) [FRA]
Located 1 voting disk(s).

Not sure whether I would dare that all in a production system, though

Conclusion: We can drop ASM Disks that contain Voting Disks as long as there are enough Disks left in the Diskgroup to retain the same number of Voting Disks (each inside a separate Failure Group) afterwards. Apparently – but: “Don’t believe it, test it!”