In-Depth

Why Physical Data Protection Isn't Enough

Logical data protection is a vital part of IT's backup/recovery plans

• By Stephen Swoyer
• 11/08/2005

There’s a potential elephant hiding in the closets of even the most meticulously conceived disaster-recovery and business-continuity planning efforts.

Sure, you specified your service level objectives (SLO) and created your physical data protection plans. But what about your logical data protection plans? Many organizations haven’t, says David Hill, a principal with storage networking an information lifecycle management (ILM) consultancy The Mesabi Group LLC. This oversight could come back to haunt them, Hill warns.

“Logical data protection insures against logical failures—such as viruses, database corruption, and inadvertent file or table deletions,” Hill explains, noting that while there are a surfeit of physical data protection strategies—e.g., RAID and remote mirroring—the same isn’t true for logical data protection.

“Physical techniques such as remote mirroring cannot protect against data corruption, since the corruption simply propagates without regard to protective measures.”

There’s always tape backup, Hill allows, but given the often stringent recovery time objectives (RTO) and recovery-point objectives (RPO) that organizations are operating under, tape is often a non-starter. “Due to its inherent limitations, restoring from tape (or even from a virtual tape library) is unlikely to meet low RTO/RPO requirements,” he points out.

There are also showstoppers associated with so-called “snapshot” backup technologies—i.e., products that capture exact, bit-for-bit replicas (or images) of a system, application, or environment—too. They provide logical protection, to be sure, but—Hill argues—probably don’t provide enough granularity.

There’s a white knight hero to this story, of course. To wit, Hill cites the emergence of a viable set of continuous data protection (CDP) products from EMC Corp., Hewlett-Packard Co., and IBM Corp. (among others) that help to address logical data protection problems. As a bonus, he suggests, some of these solutions provide an extra measure of physical protection. “CDP solutions propose to restore data to any point in time by capturing a copy of each I/O as it occurs,” says Hill. One upshot of this, superficially, is that CDP products promise tantalizing RPOs of—in some cases—zero (i.e., no loss of data).

Today’s CDP solutions aren’t silver bullets, however. They can’t guarantee a zero RTO, for example, because administrators must first perform a forensic analysis of the data to determine the precise time to which it should be restored, Hill says. There are other real-world constraints, too. “[A]dministrators may have to accept some data loss in order to restore to a point before the corruption occurred since it may be difficult to separate the good data from the bad after the corruption point took place.” That being said, Hill argues, CDP solutions more than fit the bill from both an RTO and an RPO perspective.

In addition to EMC (RestorePoint), HP (which OEMs a solution called RecoveryONE), and IBM (Tivoli Continuous Data Protection for Files), CDP products abound from smaller vendors, too. Players such as InMage (DR-Scout VX), Kashya (KBX 5000 CDP), Mendocino Software (the proprietor of Recovery ONE), Revivio (Continuous Protection System), Storactive (LiveBackup and LiveServ), TimeSpring (TimeData), and XOsoft (Enterprise Rewinder) and others all market viable CDP solutions, says Hill.

Viable, yes, but mature and established, no. “The … market is in now in its Wild Wild West phase. The next year should see the introduction of new products and the introductions of new functions and features in existing products,” Hill speculates, suggesting that vendors will focus on more tightly integrating their products into their overall data-protection portfolios. “Another focus will be on achieving greater clarity on issues that are generating heat today, such as the ability to restore to a robust consistency point.”

Nevertheless, Hill suggests, IT organizations should think twice before waiting for the dust to settle.

“That may be a grave mistake as it could perpetuate the exposure to logical data protection problems. Even though a great deal of sifting and sorting through numerous, sometimes confusing options is required, we believe that IT managers are well advised to consider and evaluate how the current generation of … solutions might fill their organizations’ data protection needs,” he concludes.