Configuring bitmap space for Copy Services or VDisk mirroring

You can use the Modify Copy Service Space panel in the SAN Volume Controller Console to modify the amount of memory that is available for the FlashCopy®, Metro Mirror, or Global Mirror Copy Services features or virtual disk (VDisk) mirroring.

The total bitmap space that is available for Copy Services features and VDisk mirroring in an I/O group is 512 MB. The following table provides an example of the amount of memory that is required for VDisk Mirroring and each Copy Service feature:
Feature Grain size 1 MB of memory provides the following VDisk capacity for the specified I/O group
Metro Mirror or Global Mirror 256 KB 2 TB of total Metro Mirror and Global Mirror VDisk capacity
FlashCopy 256 KB 2 TB of total FlashCopy source VDisk capacity
FlashCopy 64 KB 512 GB of total FlashCopy source VDisk capacity
Incremental FlashCopy 256 KB 1 TB of total incremental FlashCopy source VDisk capacity
Incremental FlashCopy 64 KB 256 GB of total incremental FlashCopy source VDisk capacity
VDisk Mirroring 256 KB 2TB of mirrored VDisk capacity
Notes:
  1. For multiple FlashCopy targets, you must consider the number of mappings. For example, for a mapping with a grain size of 256 KB, 8 KB of memory allows one mapping between a 16 GB source VDisk and a 16 GB target VDisk. Alternatively, for a mapping with a 256 KB grain size, 8 KB of memory allows two mappings between one 8 GB source VDisk and two 8 GB target VDisks.
  2. When creating a FlashCopy mapping, if you specify an I/O group other than the I/O group of the source VDisk, the memory accounting goes towards the specified I/O group, not towards the I/O group of the source VDisk.
  3. For VDisk mirroring, the full 512 MB of memory space enables 1 PB of total VDisk Mirroring capacity.
Before you specify the memory settings on the Modify Copy Service Space panel, consider the following factors.
  • For FlashCopy relationships, only the source VDisk allocates space in the bitmap table.
  • For Metro Mirror or Global Mirror relationships, two bitmaps exist. One is used for the master cluster and one is used for the auxiliary cluster, because the direction of the relationship can be reversed.
  • The smallest possible bitmap is 4 KB; therefore, a 512 byte VDisk requires 4 KB of bitmap space.

This task assumes that you have already launched the SAN Volume Controller Console.

Perform the following steps to change the amount of memory that is available for Copy Services features or virtual disk (VDisk) mirroring:

  1. Click Work with Nodes > I/O Groups in the portfolio. The Viewing Input/Output Groups panel is displayed.
  2. Select the I/O Group and select Modify Copy Services Space from the task list. Click Go. The Modify Copy Service Space panel is displayed.

    The current setting of total memory that is allocated for Global / Metro Mirror, FlashCopy, and VDisk Mirroring is displayed. The total free memory that can be allocated for Global / Metro Mirror, FlashCopy, and VDisk Mirroring is also displayed.

  3. Enter a value between 0 MB and 512 MB for the new total amount of memory to allocate for Global / Metro Mirror, FlashCopy, or virtual disk (VDisk) mirroring.
  4. Click OK to change the total bitmap space allocated for the selected Copy Services feature or VDisk mirroring in an I/O group.
Parent topic: Input/output groups
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