250 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
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. 
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 lists the bitmap space configuration options.
Table 7-1   Bitmap space default configuration
The sum of all bitmap memory allocation for all functions except FlashCopy must not exceed 
552 MiB.
Note: An unmirrored volume can be migrated from one location to another by adding a 
second volume copy at the required destination, waiting for the two copies to synchronize, 
and then removing the original copy. This operation can be stopped at any time. The two 
copies can be in different storage pools with different extent sizes. For more information, 
see 7.7.2, “Volume migration by adding a volume copy” on page 285.
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.
Copy service Minimum 
allocated 
bitmap 
space
Default 
allocated 
bitmap 
space 
Maximum 
allocated 
bitmap 
space
Minimuma capacity when 
using the default values
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. 
Remote copyb
b. Remote copy includes Metro Mirror, Global Mirror, and active-active relationships.
0 20 MiB 512 MiB 40 TiB of remote mirroring 
volume capacity
FlashCopyc
c. FlashCopy includes the FlashCopy function, Global Mirror with change volumes, and 
active-active relationships.
0 20 MiB 2 GiB /SM59000010 TiB of FlashCopy 
source volume capacity
/SM5900005 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 /SM59000080 TiB array capacity 
using RAID 0, 1, or 10
/SM59000080 TiB array capacity in 
three-disk RAID 5 array
/SM590000Slightly less than 120 TiB 
array capacity in five-disk 
RAID 6 array