Fast Mirror resync and Fast Rebalance - 11g new feature

1. Fast Mirror resync and Fast Rebalance - 11g new feature
     Fast Mirror resync and Fast Rebalance two new features available in 11g .

 Fast Mirror resync:

  ASM fast resync keeps track of pending changes to extents on an OFFLINE disk during an outage. The extents are resynced when the disk is brought back online or replaced.

By default, ASM drops a disk shortly after it is taken offline. You can set the DISK_REPAIR_TIME attribute to prevent this operation by specifying a time interval to repair the disk and bring it back online.

To use this feature, the disk group compatibility attributes must be set to 11.1 or higher
Fast Rebalance

In 11g, you can use the STARTUP RESTRICT command to control access to an ASM instance while you perform maintenance. This startup option is used to implement ASM Fast Rebalance feature. Rebalance operations that occur while a disk group is in RESTRICTED mode eliminate the lock and unlock extent map messaging between ASM instances in Oracle RAC environments.

When an ASM instance is started with 'STARTUP RESTRICT' option and is active in this mode, all of the disk groups are mounted in RESTRICTED mode which prevents databases from connecting to the ASM instance. In addition, the restricted clause of the ALTER SYSTEM statement is disabled for the ASM instance.
  Follow the below steps to do the fast rebalance
  1. startup restrict;
  2.  alter diskgroup dg1 mount restricted;
            ( we cannot mount the disk in mount mode and may get ORA-15251: only restricted mount is allowed in the ASM instance )

3.alter diskgroup dg1 rebalance;
  ( we cannot open database against the asm when it is in restrict mode,we may get the below error

ORA-01157: cannot identify/lock data file 5 - see DBWR trace file
ORA-01110: data file 5: '+DG1/11g/datafile/exy.256.627345731'

4.shutdown immediate
   ( we cannot enable restriced mode as we do in normal rdbms
     we may the below error
ORA-15000: command disallowed by current instance type
)

5.startup


2. How to improve rebalance operation when multiple disk maintenance activities are there and monitor the status of it.

  if you have multiple diskgroup managment commands like add disk /drop disks. It is recomended to run as a single command to have single rebalance operations rather than running the commands multiple times and invoke rebalances operations

  alter diskgroup diskgroup_name add disk '..../ drop disk '...' ;

Montior the sttaus of the asm operations using v$asm_operations view


SQL> desc v$asm_operation
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 GROUP_NUMBER                                       NUMBER
 OPERATION                                          CHAR(5)
 STATE                                              VARCHAR2(4)
 POWER                                              NUMBER
 ACTUAL                                             NUMBER
 SOFAR                                              NUMBER
 EST_WORK                                           NUMBER
 EST_RATE                                           NUMBER
 EST_MINUTES                                        NUMBER
 ERROR_CODE                                         VARCHAR2(44)

State of the operation:
WAIT - No operations running for the group
RUN - Operation running for the group
REAP - Operation is being run down
HALT - Operation halted by admin
ERRORS - Operation halted by errors

select state,ACTUAL ,sofar,EST_MINUTES ,operations from v$asm_operation