Consistency groups and snapshot groups are groups of pairs for which you can simultaneously perform pair tasks on all pairs within the group.
Use consistency groups to split the Thin Image Advanced pairs that are defined in the group. Splitting the pairs using the group assures data consistency at the time the storage system receives the request for storing snapshot data (splitting the pair).
For example, when you back up data constructed on multiple volumes (such as a
database), if you store snapshot data by specifying a consistency group, consistency of
the backup data is guaranteed. The following figure shows an example of backing up a
database composed of data files, control files, and log files.
A snapshot group is a group of Thin Image Advanced pairs. Use consistency or snapshot groups to perform Thin Image Advanced tasks on all of the pairs within the group. You define Thin Image Advanced pairs to a snapshot group or a consistency group when you create the pairs. You should split Thin Image Advanced pairs by using consistency groups which guarantee data consistency.
If two or more pairs in a snapshot group share the same LDEV for the P-VOLs, you cannot split the pairs at the same time by using the snapshot group. If this is the case, split the pairs one by one. Note that you can define only one pair for each P-VOL in a consistency group.
The following table shows the differences between consistency groups and snapshot groups.
Item |
Consistency group |
Snapshot group |
---|---|---|
Pair limit per group |
8,192 |
8,192 |
Group limit |
2,048 |
2,048 |
Data consistency in a group |
Guaranteed |
Not guaranteed |
Software application from which you can define pairs |
HTI Advanced, HTI, SI, and SIz |
HTI Advanced, HTI |