4
Chapter 1 Overview of Hitachi Copy Solutions
1.2.4
Hitachi Copy-on-Write Snapshot
Copy-on-Write (COW) Snapshot provides ShadowImage functionality using less capacity of the
disk storage system and less time for processing than ShadowImage. COW Snapshot enables
you to create copy pairs, just like ShadowImage, consisting of primary volumes (P-VOLs) and
secondary volumes (S-VOLs). The COW Snapshot P-VOLs are logical volumes (OPEN-V LDEVs),
but the COW Snapshot S-VOLs are virtual volumes (V-VOLs) with pool data stored in memory.
Copy-on-Write Snapshot is recommended for copying and managing data in a short time with
reduced cost. However, since only some of the P-VOL data is copied by COW Snapshot, the
data stored in the S-VOL is not guaranteed in certain cases (e.g., physical P-VOL failure).
ShadowImage copies the entire P-VOL to the S-VOL, so even if a physical failure occurs, the
P-VOL data can be recovered using the S-VOL. ShadowImage provides higher data integrity
than COW Snapshot, so you should consider the use of ShadowImage when data integrity is
more important than the copy speed or the capacity of the disk storage system.
Note:
Copy-on-Write Snapshot is available on USP V/VM and TagmaStore USP/NSC (not
9900V/9900).
For details on Copy-on-Write Snapshot operations, see the
Copy-on-Write Snapshot User’s
Guide
for the storage system, or contact your Hitachi Data Systems account team.
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Страница 180: ...162 Chapter 3 Preparing for CCI Operations ...
Страница 250: ...232 Chapter 4 Performing CCI Operations Vol Type logical unit LU type e g OPEN V OPEN 9 ...
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Страница 388: ...370 Acronyms and Abbreviations ...