Datasheet
24
Chapter 1
Using Oracle ASM
Resizing Disks in an ASM Disk Group
Sometimes when more space is needed, all a disk administrator needs to do is add that
additional space to the disk devices that are being presented for ASM to use. If this is the
case, you will want to indicate to ASM that it needs to update its metadata to represent
the correct size of the disks it’s using so you get the benefit of the additional space. This
is accomplished using the
alter diskgroup command with the resize all parameter, as
shown in this example:
alter diskgroup cooked_dgroup1 resize all;
This command will query the operating system for the current size of all of the disk
devices attached to the disk group and will automatically resize all disks in that disk group
accordingly. You can indicate that a specific disk needs to be resized by including the disk
name (from the
NAME column in V$ASM_DISK), as shown in this example:
alter diskgroup cooked_dgroup1 resize disk FILE_DISKB1;
You can also resize an entire failure group at one time:
alter diskgroup cooked_dgroup1 resize disks in failgroup DISKCONTROL2;
Manually Rebalancing Disks Assigned to an ASM Disk Group
Manually rebalancing disks within ASM is typically not required since ASM will perform
this operation automatically. However, in cases where you might want to have some more
granular control over the disk-rebalance process, you can use the
alter diskgroup com-
mand along with the
rebalance parameter to manually rebalance ASM disks.
When we discuss rebalancing disks in ASM, we often discuss the power level that is
assigned to that rebalance operation. Setting power with regard to a rebalance operation
really defines the urgency of that operation with respect to other operations occurring on
the system (for example, other databases or applications). When a rebalance operation
occurs with a low power (for example, 1, the typical default), then that operation is not
given a high priority on the system As a result, the rebalance operation can take some time.
When a higher power setting is used (for example, 11, the maximum), the ASM is given
higher priority. This can have an impact on other operations on the system. If you use a
power of 0, this will have the effect of suspending the rebalance operation. You can set the
default power limit for the ASM instance by changing the
asm_power_limit parameter.
Here is an example of starting a manual rebalance of a disk group:
alter diskgroup cooked_dgroup1 rebalance power 5 wait;
In this example, you will notice that we used the wait parameter. This makes this rebalance
operation synchronous for our session. Thus, when the SQL prompt returns, we know that
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