content_image/1001380.jpg
The FlashCopy Mapping status changes to Stopped, as shown in Figure 10-61. 

<img src='content_image/1001380.jpg'>

## 10.5 Volume mirroring and migration options 

Volume mirroring  is a simple RAID 1-type function that enables a volume to remain online, even when the storage pool that is backing it becomes inaccessible. Volume mirroring is designed to protect the volume from storage infrastructure failures by seamless mirroring between storage pools. 

Volume mirroring is provided by a specific volume mirroring function in the I/O stack, and it cannot be manipulated like a FlashCopy or other types of copy volumes. However, this feature provides migration functionality, which can be obtained by splitting the mirrored copy from the source, or by using the migrate to  function. Volume mirroring cannot control backend storage mirroring or replication. 

With volume mirroring, host I/O completes when both copies are written, and this feature is enhanced with a tunable latency tolerance. This tolerance provides an option to give preference to losing the redundancy between the two copies. This tunable timeout value is Latency  or Redundancy . 

The Latency  tuning option, which is set with chvdisk -mirrorwritepriority latency , is the default. It prioritizes host I/O latency, which yields a preference to host I/O over availability. However, you might need to give preference to redundancy in your environment when availability is more important than I/O response time. Use the chvdisk -mirror writepriority redundancy  command to set the redundancy option. 

Regardless of which option you choose, volume mirroring can provide extra protection for your environment. 

Migration offers the following options: 

GLYPH<SM590000> Export to Image mode. By using this option, you can move storage from managed  mode to image  mode, which is useful if you are using the IBM Storwize as a migration device. For example, vendor A’s product cannot communic ate with vendor B’s product, but you must migrate data from vendor A to vendor B. By using Export to image mode, you can migrate data by using Copy Services functions and then return control to the native array while maintaining access to the hosts. 

GLYPH<SM590000> Import to Image mode. By using this option, you can import a storage MDisk or logical unit number (LUN) with its data from an external storage system without putting metadata on it so that the data remains intact. After you import it, all copy services functions can be used to migrate the storage to other locations while the data remains accessible to your hosts. 

GLYPH<SM590000> Volume migration by using volume mirroring and then by using Split into New Volume. By using this option, you can use the available RAID 1 functionality. You create two copies of data that initially has a set relationship (one volume with two copies, one primary and one secondary) but then break the relationship (two volumes, both primary and no relationship between them) to make them independent copies of data. 

