Thin Image consistency group requirements

Thin Image User Guide
Version
9.8.6
Audience
anonymous
Part Number
MK-98RD9020-16

The attributes of Thin Image consistency groups, such as the pair limit and pair type, have usage requirements. Review these requirements before creating consistency groups.

Item

Requirement

Consistency group ID

Value: 0 to 2,047

With SI, SIz, HTI, and HTI Advanced, you can create up to 2,048 consistency groups in VSP 5000 series storage.

Manual assignment of a consistency group ID to an HTI pair using the paircreate command:

  • Specify a consistency group ID from 0 to 255.

Automatic assignment of a consistency group ID to an HTI pair using the paircreate or raidcom add snapshot commands:

  • Using the paircreate command, if a number is not specified, an unassigned number from 0 to 255 is automatically assigned.1
  • Using the raidcom add snapshot command, if a number is not specified, an unassigned number from 0 to 2,047 is automatically assigned.2

Consistency group ID is displayed in the following windows in HDvM - SN:

  • Consistency Groups tab in Local Replication window.
  • Consistency Group Properties window.
  • In CCI, use the raidcom get snapshot command to view the consistency group ID.

Pair limit

8,192 pairs per consistency group.

Pair type

SI, SIz, Thin Image, and Thin Image Advanced pairs cannot be contained in a single consistency group. For Thin Image consistency groups, only Thin Image pairs can be defined in a group.

Snapshot and cloned pairs cannot be contained in a single consistency group.

Notes:
  1. Thin Image assigns a number in ascending order from 0 to 255.
  2. ShadowImage uses numbers from 0 to 127. Because of this, Thin Image assigns an unassigned number from 128 to 2,047 first. If there is no unassigned number from 128 to 2,047, then Thin Image assigns an unassigned number from 0 to 127.

Consistency group restrictions:

  • Thin Image pairs that share P-VOLs or are in higher and lower layers of a snapshot tree cannot be defined in the same consistency group. If they are defined in the same consistency group, the raidcom add snapshot command is rejected.
  • Do not place pairs that are not in consistency groups, in a group defined by the CCI configuration definition file. If these pairs are in the same group, the pairsplit command may terminate and the snapshot data may not be the P-VOL data generated when a storage system received the pairsplit command.
  • Only one consistency group can be specified for a group defined in the CCI configuration definition file.
  • When a pair for which a consistency group is specified and is already created, if you specify another consistency group to create a pair, the pair is added to the same consistency group.
  • To specify multiple consistency groups, use the CCI configuration definition file to define the same number of groups as the consistency groups you want to specify.