HP XP RAID Manager Software - Manual (Page 6)

1 Overview
Unless otherwise specified, the term P9000 in this guide refers to the following disk array:
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P9500 Disk Array
The GUI illustrations in this guide were created using a Windows computer with the Internet Explorer
browser. Actual windows may differ depending on the operating system and browser used. GUI
contents also vary with licensed program products, storage system models, and firmware versions.
With Snapshot, you create virtual copies of a data volume in the P9500.
This guide provides instructions for planning and designing, configuring, operating, monitoring,
and troubleshooting Snapshot.
Snapshot software
Snapshot creates a virtual, point-in-time copy of a data volume. Since only changed data blocks
are stored in the Snapshot storage pool, storage capacity is substantially less than the source
volume. This results in significant savings compared with full cloning methods
The most probable types of target applications for Snapshot are:
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Database copies for decision support/database inquiries
•
Non-disruptive backups from a Business Copy secondary volume
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Periodic point-in-time disk copies for rapid restores in the event of a corrupted data volume
How Snapshot works
With Snapshot, you create a volume “pair” when you:
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Select a volume that you want to replicate.
•
Identify another volume that will contain the copy.
•
Associate the primary and secondary volumes.
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Set up a data pool.
•
Create the pair.
The primary volume (P-VOL) can continue being updated once a pair is made. The virtual volume
(V-VOL) points to the data in the P-VOL as it exists at the moment.
When a pair is split, the P-VOL continues being updated, but the V-VOL stops mirroring the current
P-VOL. Instead, it maintains a point-in-time virtual copy, from the time of the split. When new data
is to be written to the P-VOL, Snapshot maintains the point-in-time image by copying the data that
is to be changed to the data pool. The V-VOL, which contains no actual data, points to the
point-in-time data in the P-VOL and data pool.
When the pair is resumed, pool data is deleted.
Volume pairs — P-VOLs and V-VOLs
A pair consists of a primary volume (P-VOL), which contains the original data, and from 1 to 64
virtual volumes (V-VOLs), which contain virtual copies of the P-VOL. The P-VOL and its V-VOL(s) are
located in the same storage system. A V-VOL is also referred to as a secondary volume (S-VOL).
Unlike the P-VOL, which contains actual data, the V-VOL is made up of pointers to the data in the
P-VOL, and, when the pair is split, to original data moved to the data pool as the P-VOL is updated.
The figure below illustrates Snapshot volumes and data pool interaction during a split.
Though V-VOLs must be set up with the same capacity as the paired P-VOL, the capacity is not
actually used and remains available as free storage capacity. This V-VOL sizing requirement (must
be equal to the P-VOL), is necessary for Snapshot and storage system logic. Also, V-VOL pointers
6 Overview