Consistency Groups - Hitachi AMS 2000 User Manual

Consistency groups

Application data often spans more than one volume. With TCE, it is possible
to manage operations spanning multiple volumes as a single group. In a
consistency group (CTG), all primary logical volumes are treated as a single
entity.
Managing primary volumes as a consistency group allows TCE operations to
be performed on all volumes in the group concurrently. Write order in
secondary volumes is guaranteed across application logical volumes.
Figure 1-3
•
In this illustration, observe the following:
• The P-VOLs belong to the same consistency group. The host updates
the P-VOLs as required (1).
• The local array identifies the differential data in the P-VOLs when the
cycle is started (2) in an atomic manner. The differential data of the
group of the P-VOLs are determined at time T2.
• The local array transfers the differential data to the corresponding S-
VOLs (3). When all differential data is transferred, each S-VOL is
identical to its P-VOL at time T2 (4).
• If pairs are split or deleted, the local array stops the cycle update for
the consistency group. Differential data between P-VOLs and S-VOLs is
determined at that time. All differential data is sent to the S-VOLs, and
the split or delete operations on the pairs completes. S-VOLs maintain
1–6
Hitachi AMS 2000 Family TrueCopy Extended Distance User Guide
shows TCE operations with a consistency group.
Figure 1-3: TCE Operations with Consistency Groups
Overview