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. Table 7-1 Bitmap space default configuration Copy service Minimum  allocated  bitmap  space Default  allocated  bitmap  space  Maximum  allocated  bitmap  space Minimum $^{a}$  capacity when  using the default values Remote copy b 0 20 MiB 512 MiB 40 TiB of remote mirroring  volume capacity FlashCopy c 0 20 MiB 2 GiB GLYPH<SM590000> 10 TiB of FlashCopy  source volume capacity GLYPH<SM590000> 5 TiB of incremental  FlashCopy source volume  capacity Volume  mirroring 0 20 MiB 512 MiB 40 TiB of mirrored volumes RAID 0 40 MiB 512 MiB GLYPH<SM590000> 80 TiB array capacity  using RAID 0, 1, or 10 GLYPH<SM590000> 80 TiB array capacity in  three-disk RAID 5 array GLYPH<SM590000> Slightly less than 120 TiB  array capacity in five-disk  RAID 6 array 272  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 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.