Typically, you should increase reserved capacity when you receive a warning that the reserved capacity for a mirrored pair is becoming full. You can increase reserved capacity only in increments of 8 GiB.
For asynchronous mirroring operations, reserved capacity is typically 20 percent of the base volume. Choose a larger capacity for reserved capacity if one or both of these conditions exist:
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You intend to keep the mirrored pair for a long period of time.
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A large percentage of data blocks will change on the primary volume due to heavy I/O activity. Use historical performance data or other operating system utilities to help you determine typical I/O activity to the primary volume.
You can increase the reserved capacity for a mirrored pair by performing one of these actions:
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Adjust the capacity percentage for a mirrored pair volume by selecting and then clicking the Reserved Capacity tab.
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Create a new volume using free capacity that is available on a pool or volume group.
If no free capacity exists on any pool or volume group, you can add unconfigured capacity in the form of unused drives to a pool or volume group.