2–2 Planning and Design
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
The Plan and Design Workflow
The SnapShot planning effort consists of finding the number of V-VOLs your
organization requires for the P-VOL, the V-VOL(s)’ lifespan — how long they
must be held before being updated again — the frequency that snapshots
are taken, and the size of the data pool. The answers are determined by
analyzing the organization’s business needs and measuring the write
workload that is generated by the host application.
The plan and design workflow consists of the following:
• Assess business needs.
• Determine how often a snapshot should be taken.
• Determine how long the snapshot should be held.
• Determine the number of snapshot copies required per P-VOL.
• Measure production system write workload.
• Size the data pool. (For a description of the data pool, see Data Pools
on page 1-6.
These objectives are addressed in detail in this chapter. Two other tasks are
required before your design can be implemented. These are also addressed
in this chapter.
• When you have established your SnapShot system design, the system’s
maximum allowed capacity must be calculated. This has to do with how
the Storage system manages segments.
• Equally important in the planning process are the ways that various
operating systems interact with SnapShot. Make sure to review the
information at the end of the chapter.
Assessing Business Needs
Business needs have to do with how long back-up data needs to be retained
and what the business or organization can tolerate when disaster strikes.
These organizational priorities help determine the following:
• How often a snapshot should be made (frequency)
• How long a snapshot (the V-VOL) should be held (lifespan)
• The number of snapshots (V-VOLs) that will be required for the P-VOL.

Establishing How Often a Copy Is Made (Copy Frequency)

The frequency that copies need to be made is determined by how much data
can be lost in a disaster before business is significantly impacted.
To determine how often a snapshot should be taken
• Using knowledge of your business, decide how much data could be lost
in a disaster without significant impact to the business.