Faster disks are added as a new failure group in the existing disk group with the slower
disks and the automatic rebalance occurs. After the rebalance operations complete, the failure
groups containing the slower disks are dropped, leaving a disk group with only fast disks. To
make this operation even faster, both the add and drop operations can be initiated within the
same alter diskgroup command.
As an example, suppose you want to create a new disk group with high redundancy to hold
tablespaces for a new credit card authorization. Using the view V$ASM_DISK, you can view all
Chapter 4: Physical Database Layouts and Storage Management 109
disks discovered using the initialization parameter ASM_DISKSTRING, along with the status of
the disk (in other words, whether it is assigned to an existing disk group or is unassigned). Here
is the command:
SQL> select group_number, disk_number, name,
2 failgroup, create_date, path from v$asm_disk;
GROUP_NUMBER DISK_NUMBER NAME FAILGROUP CREATE_DA PATH
------------ ----------- ---------- ---------- --------- ---------------
0 0 /dev/raw/raw8
0 1 /dev/raw/raw7
0 2 /dev/raw/raw6
0 3 /dev/raw/raw5
2 1 RECOV_0001 RECOV_0001 08-JUL-07 /dev/raw/raw4
2 0 RECOV_0000 RECOV_0000 08-JUL-07 /dev/raw/raw3
1 1 DATA_0001 DATA_0001 08-JUL-07 /dev/raw/raw2
1 0 DATA_0000 DATA_0000 08-JUL-07 /dev/raw/raw1
8 rows selected.
SQL>
Out of the eight disks available for ASM, only four of them are assigned to two disk groups,
DATA and RECOV, each in its own failure group.
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