Consistency Group (Ctg); Differential Management Lus (Dmlu); Lu Ownership Of P-Vols And Data Pools - Hitachi AMS2100 User Manual

Consistency group (CTG)

Differential Management LUs (DMLU)

LU Ownership of P-VOLs and data pools

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Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
Application data often spans more than one volume. With SnapShot,
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 SnapShot primary volumes as a consistency group allows
multiple operations to be performed on grouped volumes
concurrently. Write order is guaranteed across application logical
volumes, since snapshots can be taken at the same time.
The DMLU is an exclusive volume used for storing SnapShot
information when the array system is powered down. The DMLU is
treated the same as other volumes in the storage system, but is
hidden from a host. The DMLU requires user setup. See
the Differential Management LU (DMLU) on page 5-5
The load balancing function is not applied to the LUs specified as a
SnapShot pair.
The ownership of the LU specified in the S-VOl of the SnapShot pair
is the same as the ownership of the LU specified in the data pool. This
ownership change operates regardless of the setting status of load
balancing.
For example, if creating a SnapShot pair by specifying the LU whose
ownership is controller 0 as a P-VOL and assigned the LU whose
ownership is controller 1 as a data pool, the ownership of the LU
specified in the P-VOL is changed to controller 1.
If two or more SnapShot pairs share the same data pool, the
ownerships of all the pairs are biased toward the same controller and
the load is concentrated. To diversify the load, create two or more
data pools whose ownerships differ, and specify the data pool to be
equal when creating a SnapShot pair.
SnapShot overview
Setting up
for details.