What is going behind the screen when a member disk is dropped?

alter diskgroup DG_DBA_DD501 drop disk DG_DBA_DD501_0008

By default, the rebalance power is 1. 

Wed Jan 12                                                                                                       page    1
                                   Long-Running ASM Operations (From V$ASM_OPERATIONS)

                                                                     Est
                                                                    Time
   ASM ASM                   ASM     ASM     AUs     AUs     AUs   Until
  Disk Oper-    ASM        Power   Power   To Be   Moved   Moved    Done
 Grp # ation    State      Rqstd   Alloc   Moved  So Far   PerMI    (MM)
------ -------- -------- ------- ------- ------- ------- ------- -------
1         REBAL    RUN            1       1   53381   12520    1751      23


 Since the server is idle, I want it to run faster, I pumped the rebalance level to 5.  ASM rebalance process is interrupted and regenerate 5 rebalanced processes.  We can see 5 trace files with in ASM udump directory.

SQL> alter diskgroup DG_DBA_DD501 rebalance power 5;

Wed Jan 12                                                                                                       page    1
                                   Long-Running ASM Operations (From V$ASM_OPERATIONS)

                                                                     Est
                                                                    Time
   ASM ASM                   ASM     ASM     AUs     AUs     AUs   Until
  Disk Oper-    ASM        Power   Power   To Be   Moved   Moved    Done
 Grp # ation    State      Rqstd   Alloc   Moved  So Far   PerMI    (MM)
------ -------- -------- ------- ------- ------- ------- ------- -------
     1 REBAL    RUN            5       5    8697      82    4100       2


-rw-r-----   1 oracle   oinstall      11269 Jan 12 19:30 +asm1_arb0_340204.trc
-rw-r-----   1 oracle   oinstall      13970 Jan 12 19:52 +asm1_arb1_340210.trc
-rw-r-----   1 oracle   oinstall      14329 Jan 12 19:52 +asm1_arb0_1028188.trc
-rw-r-----   1 oracle   oinstall      14223 Jan 12 19:52 +asm1_arb2_893148.trc
-rw-r-----   1 oracle   oinstall      13909 Jan 12 19:52 +asm1_arb4_479426.trc
-rw-r-----   1 oracle   oinstall      14087 Jan 12 19:52 +asm1_arb3_213194.trc

The trace file looks something like this..

ARB1 relocating file +DG_DBA_DD501.594.663762503 (102 entries)
ARB1 relocating file +DG_DBA_DD501.595.663762509 (1 entries)
ARB1 relocating file +DG_DBA_DD501.596.663762517 (120 entries)
*** 2011-01-12 19:41:02.287
ARB1 relocating file +DG_DBA_DD501.598.663762523 (120 entries)
*** 2011-01-12 19:41:13.662
ARB1 relocating file +DG_DBA_DD501.600.663762533 (120 entries)


When the rebalance is finished, all ARB processes stopped, the disk is emptied and it was brought offline.  The ASM diskgroup is updated with member information and then the disk hear is erased.

Wed Jan 12 19:52:10 2011
NOTE: stopping process ARB3
NOTE: stopping process ARB1
NOTE: stopping process ARB4
NOTE: stopping process ARB2
NOTE: stopping process ARB0
Wed Jan 12 19:52:14 2011
SUCCESS: rebalance completed for group 1/0xe01e0de1 (DG_DBA_DD501)
Wed Jan 12 19:52:14 2011
SUCCESS: rebalance completed for group 1/0xe01e0de1 (DG_DBA_DD501)
NOTE: PST update: grp = 1
SUCCESS: grp 1 disk DG_DBA_DD501_0008 emptied
WARNING: offlining disk 8.3933142294 (DG_DBA_DD501_0008) with mask 0x1
NOTE: PST update: grp = 1, dsk = 8, mode = 0x6
NOTE: cache closing disk 8 of grp 1: DG_DBA_DD501_0008
NOTE: PST update: grp = 1
NOTE: erasing header on grp 1 disk DG_DBA_DD501_0008
NOTE: cache closing disk 8 of grp 1: DG_DBA_DD501_0008



The header status of the dropped disk was changed from MEMBER to FORMER.  We can remove a FORMER disk.

DISKGROUP       DISK# DISKNAME                 TOTAL_MB      FREE_MB PATH                                HEADER_STATU
--------------- ----- -------------------- ------------ ------------ ----------------------------------- ------------
                    0                            32,768            0 /dev/dg_dba_dd501_disk12            FORMER

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