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Disaster recovery relief

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Problems with disk-to-disk split mirrors

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The limited protection and recoverability of point-in-time snapshots
  • The time between snapshots increases the data risk exposure
  • More snapshots reduce exposure, but also reduce inefficient use of additional storage (requires two to nine times the original storage space)
Storage vendor array lock-in
  • Must use the same--or a more expensive--storage array as the remote replication or snapshot catcher
The performance across a TCP/IP WAN
  • TCP/IP WAN issues (congestion, BER, jitter, latency) can reduce throughput performance by one to two orders of magnitude, reducing backup window success
Everyone is aware that in an era of natural disasters, terrorism and regulations, disaster recovery (DR) and business continuity processes are essential. But the high cost of DR and business continuity tools prohibits many organizations from implementing them. In fact, the cost of these tools is often greater than the value of the data that's being protected. Expensive DR tools put you in the precarious position of having to provide enough DR and business continuity to satisfy regulations, but not having enough to meet your real needs.

Compounding the problem is that many storage administrators don't know how to effectively implement traditional DR and business continuity solutions. Their organizational policy may be to back up to tape once a night, and perhaps even have that tape picked up by a service every day. Of course, there's a good chance that the operator didn't change the tape when the job said it was full, overwriting previous data. Fortunately, numerous storage vendors are starting to develop simpler, innovative and more cost-effective DR and business continuity products.

DR pain threshold
Cost, complexity and effectiveness all contribute to how high or low the pain threshold is for a specific DR solution.

Cost: The most common complaint about DR practices is that they require significant capital and operating investment. Disk-to-disk or split mirror products require the capital expense (CapEx) of a complete duplication of storage. When multiple split mirrors or point-in-time snapshots are implemented (such as EMC Corp's Symmetrix Remote Data Facility and TimeFinder), the CapEx increases exponentially. Add in the ongoing operating expenses (OpEx) of software licenses, maintenance, personnel time, training and network, and the costs can quickly overwhelm the value of the protected data.

Even traditional tape backup products can prove to be far more costly than the data they protect. The CapEx may be lower (tape drives, automated tape libraries and tape media) than disk-to-disk solutions, yet the OpEx is significantly greater. This is because the amount of human errors, failed backups, gaps in the data, lost tapes, broken tapes and missed backup windows are typically much higher than is generally acknowledged.

Complexity:If cost is the No. 1 DR and business continuity complaint, complexity is a close second. A survey of more than 200 enterprise and small- to medium-sized businesses conducted last year by Dragon Slayer Consulting, Beaverton, OR, revealed a startlingly high level of user-perceived complexity and frustration with tape backup and recovery (see "DR is too complex "). There were similar levels of frustration (53%) with disk-to-disk split mirroring.

Effectiveness: Effectiveness defines how well a goal or task is completed. For DR and business continuity, this breaks down into two main points: the effectiveness of the data protection and the effectiveness of data recovery.

There's a significant difference in the level of pain between traditional tape backup and recovery and disk-to-disk split mirrors. Only 37% of the tape users in the survey were satisfied--or somewhat satisfied--with the effectiveness of their solution, whereas the satisfaction numbers for the disk-to-disk split mirror users was 68%.

This was first published in April 2004

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