This is the fifth of eight in a series titled 8 Must Haves for the IT Director

Number 5 – Space-Efficient Snapshots

The hidden cost of snapshot space hogs

Using snapshots to protect array data is nothing new. What is new is how the aging (or tiered progression) algorithms associated with primary data can also be applied to snapshot data. There are 2 parts to snapshot efficiency; 1) minimizing the amount needed initially and 2) placing the older snapshots on lower tiered groups of disks.

Some storage architectures implement snapshots using large chunks, or pages, of data. These larger block approaches tend to overuse snapshot space by preserving data at a minimum of 15K chunks. Imagine a 15K snapshot for a single byte change. Compellent snapshots can be configured from 512 Byte blocks to 4K, drastically reducing the per change overhead.

Snapshot migration reduces costs

The second snapshot efficiency gained by the Compellent architecture is that, similar to primary data, snapshot data can also be progressively moved to lower speed, lower cost media as it ages. Snapshots for yesterday are generally more likely to be needed than snapshots from a previous month, especially for high-IO applications. Thus, it makes sense that the most recent snapshots are readily available on the fastest tier groups; a process handled automatically by Compellent.

Since Replays are so space efficient, recovery can take as few as 10 seconds and volumes can be
mapped to any server without disruption. To simplify the process, administrators set up Replay
schedules using an intuitive point-and-click interface. Replays can also be used to test new applications
and service packs on actual data without risk, efficiently support boot-from-SAN operations and
virtually eliminate backup windows on production systems.


Next up in our 8 Must Have series is #6, Thin Replication.

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