Actions you can perform on volumes
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You can perform a number of different actions on a volume: increasing capacity, deleting, copying, initializing, redistributing, changing ownership, changing cache settings, and changing media scan settings.
Increase capacity
You can expand the capacity for a volume in two ways:
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Use the free capacity that is available in the pool or volume group.
You add capacity to a volume by selecting .
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Add unassigned capacity (in the form of unused drives) to the pool or volume group of the volume. Use this option when no free capacity exists in the pool or volume group.
You add unassigned capacity to the pool or volume group by selecting .
If free capacity is not available in the pool or volume group, you cannot increase the capacity of the volume. You must increase the size of the pool or volume group first or delete unused volumes.
After you expand the volume capacity, you must manually increase the file system size to match. How you do this depends on the file system you are using. See your host operating system documentation for details.
Delete
Typically, you delete volumes if the volumes were created with the wrong parameters or capacity, no longer meet storage configuration needs, or are snapshot images that are no longer needed for backup or application testing. Deleting a volume increases the free capacity in the pool or volume group.
Deleting volumes causes loss of all data on those volumes. Deleting a volume will also delete any associated snapshot images, schedules, and snapshot volumes and remove any mirroring relationships.
Copy
When you copy volumes, you create a point-in-time copy of two separate volumes, the source volume and the target volume, on the same storage array. You can copy volumes by selecting .
Initialize
Initializing a volume erases all data from the volume. A volume is automatically initialized when it is first created. However, the Recovery Guru might advise that you manually initialize a volume to recover from certain failure conditions. When you initialize a volume, the volume keeps its WWN, host assignments, allocated capacity, and reserved capacity settings. It also keeps the same Data Assurance (DA) settings and security settings.
You can initialize volumes by selecting .
Redistribute
You redistribute volumes to move volumes back to their preferred controller owners. Typically, multipath drivers move volumes from their preferred controller owner when a problem occurs along the data path between the host and storage array.
Most host multipath drivers attempt to access each volume on a path to its preferred controller owner. However, if this preferred path becomes unavailable, the multipath driver on the host fails over to an alternate path. This failover might cause the volume ownership to change to the alternate controller. After you have resolved the condition that caused the failover, some hosts might automatically move the volume ownership back to the preferred controller owner, but in some cases, you might need to manually redistribute the volumes.
You can redistribute volumes by selecting .
Change volume ownership
Changing the ownership of a volume changes the preferred controller ownership of the volume. The preferred controller owner of a volume is listed under .
You can change the ownership of a volume by selecting .
Mirroring and volume ownership
If the primary volume of the mirrored pair is owned by controller A, then the secondary volume will also be owned by controller A of the remote storage array. Changing the primary volume's owner will automatically change the owner of the secondary volume to ensure that both volumes are owned by the same controller. Current ownership changes on the primary side automatically propagate to corresponding current ownership changes on the secondary side.
If a mirror consistency group contains a local secondary volume and the controller ownership is changed, the secondary volume is automatically transferred back to its original controller owner on the first write operation. You cannot change the controller ownership of a secondary volume by using the Change ownership option.
Copy volume and volume ownership
During a copy volume operation, the same controller must own both the source volume and the target volume. Sometimes both volumes do not have the same preferred controller when the copy volume operation starts. Therefore, the ownership of the target volume is automatically transferred to the preferred controller of the source volume. When the volume copy is completed or is stopped, ownership of the target volume is restored to its preferred controller.
If ownership of the source volume is changed during the copy volume operation, ownership of the target volume is also changed. Under certain operating system environments, it might be necessary to reconfigure the multipath host driver before an I/O path can be used. (Some multipath drivers require an edit to recognize the I/O path. Refer to your driver documentation for more information.)
Change cache settings
Cache memory is an area of temporary volatile storage (RAM) on the controller that has a faster access time than the drive media. If you use cache memory, you can increase overall I/O performance because of these reasons:
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Data requested from the host for a read might already be in the cache from a previous operation, thus eliminating the need for drive access.
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Write data is written initially to the cache, which frees the application to continue instead of waiting for the data to be written to the drive.
Select to change the following cache settings:
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Read and write caching — The read cache is a buffer that stores data that has been read from the drives. The data for a read operation might already be in the cache from a previous operation, which eliminates the need to access the drives. The data stays in the read cache until it is flushed.
The write cache is a buffer that stores data from the host that has not yet been written to the drives. The data stays in the write cache until it is written to the drives. Write caching can increase I/O performance.
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Write caching with mirroring — Write caching with mirroring occurs when the data written to the cache memory of one controller is also written to the cache memory of the other controller. Therefore, if one controller fails, the other can complete all outstanding write operations. Write cache mirroring is available only if write caching is enabled and two controllers are present. Write caching with mirroring is the default setting at volume creation.
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Write caching without batteries — The write caching without batteries setting lets write caching continue even when the batteries are missing, failed, discharged completely, or not fully charged. Choosing write caching without batteries is not typically recommended, because data might be lost if power is lost. Typically, write caching is turned off temporarily by the controller until the batteries are charged or a failed battery is replaced.
This setting is available only if you enabled write caching. This setting is not available for thin volumes.
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Dynamic read cache prefetch — Dynamic cache read prefetch allows the controller to copy additional sequential data blocks into the cache while it is reading data blocks from a drive to the cache. This caching increases the chance that future requests for data can be filled from the cache. Dynamic cache read prefetch is important for multimedia applications that use sequential I/O. The rate and amount of data that is prefetched into cache is self-adjusting based on the rate and request size of the host reads. Random access does not cause data to be prefetched into cache. This feature does not apply when read caching is disabled.
For a thin volume, dynamic cache read prefetch is always disabled and cannot be changed.
Change media scan settings
Media scans detect and repair media errors on disk blocks that are infrequently read by applications. This scan can prevent data loss from occurring if other drives in the pool or volume group fail as data for failed drives is reconstructed using redundancy information and data from other drives in the pool or volume group.
Media scans run continuously at a constant rate based on the capacity to be scanned and the scan duration. Background scans may be temporarily suspended by a higher priority background task (for example, reconstruction), but will resume at the same constant rate.
You can enable and set the duration over which the media scan runs by selecting .
A volume is scanned only when the media scan option is enabled for the storage array and for that volume. If redundancy check is also enabled for that volume, redundancy information in the volume will be checked for consistency with data, provided that the volume has redundancy. Media scan with redundancy check is enabled by default for each volume when it is created.
If an unrecoverable medium error is encountered during the scan, data will be repaired using redundancy information, if available. For example, redundancy information is available in optimal RAID 5 volumes, or in RAID 6 volumes that are optimal or only have one drive failed. If the unrecoverable error cannot be repaired using redundancy information, the data block will be added to the unreadable sector log. Both correctable and uncorrectable medium errors are reported to the event log.
If the redundancy check finds an inconsistency between data and the redundancy information, it is reported to the event log.