content_image/993295.jpg
If the mirrored volume needs resynchronization, the system copies to the out-of-sync volume copy only these 256 kibibyte (KiB) grains that were written to (changed) since the synchronization was lost. This approach is known as an incremental synchronization  and it minimizes the time that is required to synchronize the volume copies. 

Tip:  An unmirrored volume can be migrated from one location to another as follows: You add a second volume copy at the required destination, then wait for the two copies to synchronize, and then finally remove the original copy. This operation can be stopped at any time. The two copies can be in different storage pools with different extent sizes. See 7.8.2, “Volume migration by adding a volume copy” on page 309 

A volume with more than one copy can be checked to see whether all of the copies are identical or consistent. If a medium error is encountered while it is reading from one copy, it is repaired by using data from the other copy. This consistency check is performed asynchronously with host I/O. 

Important:  Mirrored volumes can be taken offline if no quorum disk is available. This behavior occurs because the synchronization status of mirrored volumes is recorded on the quorum disk. 

Mirrored volumes use bitmap space at a rate of 1 bit per 256 KiB grain, which means that 1 MiB of bitmap space supports up to 2 TiB of mirrored volumes. The default size of bitmap space is 20 MiB, which enables up to 40 TiB of mirrored volumes. If all 512 MiB of variable bitmap space is allocated to mirrored volumes, 1 PiB of mirrored volumes can be supported. Table 7-1 shows the bitmap space configuration options. 

<img src='content_image/993295.jpg'>

a. The actual amount of available capacity might increase based on settings such as grain size and strip size. RAID is subject to a 15% margin of error. 

b. Remote copy includes Metro Mirror, Global Mirror, and active-active relationships. 

c. FlashCopy includes the FlashCopy function, Global Mirror with change volumes, and active-active relationships. 

