HP XP RAID Manager Software - Manual (Page 7)

1 Overview of Business Copy/Snapshot
With Snapshot (SS), you can create virtual copies of a data volume in the P9500 storage system.
This chapter provides instructions for planning and designing, configuring, operating, monitoring,
and troubleshooting SS.
Snapshot software
SS creates a virtual, point-in-time copy, or snapshot, of a data volume. Since only changed data
blocks are stored in the SS 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 SS are:
•
Database copies for decision support and database inquiries.
•
Non-disruptive backups from an SS secondary volume (S-VOL).
•
Periodic point-in-time disk copies for rapid restores in the event of a corrupted data volume.
How Business Copy/Snapshot works
You create a volume pair when you complete the following:
1. Select the volume that you want to replicate.
2. Identify another volume that will contain the copy.
3. Associate the primary volume (P-VOL) and S-VOLs.
4. Set up a data pool.
5. Create the pair.
The P-VOL is updated. The virtual volume (V-VOL) points to the point-in-time data in the P-VOL
and data pool and mirrors it. The V-VOL contains a virtual copy of the P-VOL; it does not
contain actual data.
For more information about creating pairs, see “Pair creation” (page 35) .
6. Split the pair.
The storage system continues to update the P-VOL. The V-VOL stops mirroring the current P-VOL.
Instead, the V-VOL maintains a snapshot from the time of the split.
For more information about splitting pairs, see “Pair split” (page 40) .
7. Write data to the P-VOL.
SS maintains the point-in-time image by copying the existing data to the data pool.
8. Resume the pair.
The pool data is deleted.
Volume pairs: P-VOLs and V-VOLs
A volume pair consists of a P-VOL, which contains the original and actual data, and at least one
and up to 64 V-VOLs. The V-VOL is made up of pointers to the data in the P-VOL. The P-VOL and
its V-VOLs are located in the same storage system. A V-VOL is also referred to as an S-VOL.
Although you must set up V-VOLs 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 is
necessary for SS and the storage system logic. The V-VOL pointers to data in the data pool and
P-VOL reside in cache memory. Enabling your system’s cache reserves part of your system’s cache
for SS.
Splitting the volume pair moves the original data to the data pool as the P-VOL is updated. The
following figures show SS volumes and data pool interaction when you split the pair.
Snapshot software 7