1–6 SnapShot Overview
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
Data Pools
After a snapshot, the V-VOL maintains a static copy of the P-VOL even as
new writes are updating the P-VOL. To do this, before an updated block is
written to the P-VOL, SnapShot sends the data that is being replaced to the
data pool. Pointers in the V-VOL are updated to locate the replaced data that
is now located in the data pool, thus maintaining the V-VOL point-in-time
image of the P-VOL.
The data pool’s function in the SnapShot process is illustrated in Figure 1-2.
Up to 64 data pools can be set for each controller. Each data pool can be
assigned to two or more P-VOLs plus the differential data of two or more V-
VOLs.
Differential Management LUs (DM-LU)
The DM-LU is an exclusive volume used for storing SnapShot information
when the array system is powered down. The DM-LU is treated the same as
other volumes in the storage system, but is hidden from a host. The DM-LU
is set at the factory at 10 GB. User configuration is not required
Consistency Group (CTG)
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.
SnapShot Interface—Storage Navigator Modular 2
Use Storage Navigator Modular 2 (Navigator 2) on the workstation to
perform SnapShot tasks. Configure, operate, and monitor SnapShot
functions with either of two interfaces: a graphical user interface (GUI) or a
Command Line Interface (CLI). Instructions in this guide refer to both
interfaces.
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CAUTION!Storage Navigator 2 CLI is provided for users with significant
storage management expertise. Improper use of this CLI could void your
Hitachi Simple Modular Storage 100 system warranty. Please consult with
your reseller before using CLI.