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Deliver High Speed CDP with SATA Disk: Here’s How It Is Done

There is a perception among enterprise organizations that in order to deploy continuous data protection (CDP) technology, they also need to use high performance disk in conjunction with it. But enterprises probably should re-assess that assumption. The emergence of new and better CDP architectures such as what InMage offers enables organizations to deliver high speed CDP while using slower performing SATA disk drives.

The belief that CDP software needs high performance disk stems from its early generations of this software. This software sat in the application server’s data path and needed high performance disk for two reasons.

First, the application generated a large number of write I/Os so the CDP needed high performance disk to keep up with the traffic. Second, and maybe more importantly, enterprises expected to recover the application on the disk used by the CDP solution. In order to ensure the application had the same performance characteristics it did in production, high performance disk was used.

So what has changed from an architectural perspective in CDP software that would no longer cause these assumptions to hold true? In the case of some products, not much has changed and these assumptions still hold true.

However in the case of InMage, it introduces a CDP architecture that minimizes the need for high performance disk drives. Rather than trying to write the data to disk as application write I/Os occur, InMage creates a two tier architecture.

On the first tier, InMage dumps the data directly to a cache that is on the InMage appliance. Only once it is cached there does it get replicated directly to InMage’s second tier, the target which acts as the retention log and holds the data.

This two tier architecture of InMage enables enterprises to protect high performance applications while using low cost, high capacity disk on the back end. InMage accomplishes this by completely decoupling the speed of the disk of the target from the performance requirements of the other appliance that captures the data.

Granted, the performance of data capture is impacted by speed of the cache on the InMage appliance. However the cache in the InMage appliance’s main memory already runs faster than any high performance disk.

So is there ever a need for high performance disk in the InMage architecture? There is, but it is only under a very specific application recovery condition. That condition is: if an organization wants to generate an image of that application, mount that image and run it as it is in production.

This situation primarily presents itself when an organization fails an application over to a disaster recovery (DR) site. In this circumstance, the primary site is gone and you want to bring up an application like Microsoft Exchange and expect to run it at the DR site until you get your production site back online. In this case, disk speed matters as it will likely impact Exchange’s performance once it is recovered.

Even in this circumstance, there may be ways to protect Exchange without having to put all of its data on high performance disk. The main determinant as to whether or not you need high performance disk is how long the organization can tolerate Exchange operating at less than optimal levels.

If the organization can tolerate a few hours of subpar Exchange performance, you may still be able to use SATA disk to recover Exchange. This configuration permits an initial, fast recovery of Exchange on SATA disk even as InMage concurrently copies the Exchange data to higher performing disk. Once the copy is complete, Exchange can then be failed over to the higher performing disk.

Organizations need to re-examine any assumptions they may have that they can only implement CDP for write intensive applications using high performance disk. InMage’s two tier architecture minimizes or even eliminates this need by giving organizations the flexibility to use slower performing disk even with their highest performing applications. In so doing, organizations can extend the benefits of CDP to the applications that really need it without breaking the bank in order to accomplish it.


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