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Disk-based backups are more forgiving

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Increasingly, customers are turning to backup-to-disk (B2D) solutions to help address their backup challenges. Benefits include:

Faster restore times due to the random access nature of disk
Fewer backup failures due to tape drive, library and media failures
More consistent backup throughput rates, as there's no backhitching effect found in tape drives when throughput drops below a given threshold
Elimination of multiplexing, simplifying backup configuration
In theory, tape can still meet or exceed the write performance of disk. However, users are finding that B2D solutions result in higher average write throughput, thus helping them shorten their backup windows. The higher throughput rates are attributable to the disk's random access, allowing users to optimize write I/O at any speed, thereby requiring significantly less tuning effort.
Getting backups to complete before the new business day starts is an ongoing challenge. The advantages of faster tape drives and increased network bandwidth are often offset by the ever-increasing amount of storage to be backed up each night.

When backups are allowed to run indefinitely until they are complete, the following bad things happen:

  • Degraded performance of backup clients during business hours
  • Inability to start the next night's backup because the previous night's backups are still running
  • Maintenance windows for the backup server and tape libraries may be lost
  • Increased likelihood of encountering open files, which are frequently skipped by backup applications
Given the many variables in the average backup environment, there isn't one best method for reducing backup windows. Before adding new functionality or architectures, it's important to identify where the bottlenecks are, understand the benefits of a shorter backup window and forecast the growth of backup data. Investing some time to understand data retention and recovery requirements can pay dividends in terms of managing the amount of data that needs to be backed up. Also, developing a plan for peak backup performance requires a solid grasp of your backup application's capabilities, including how it moves data and how it can leverage disk and its performance tuning options.

There are two fundamental ways to shorten a backup window: reduction and elimination. Reducing the amount of data to be backed up decreases backup durations by up to 50% or greater. The elimination approach makes use of snapshots and point-in-time (PIT) copies to shrink the backup window to just minutes.

This was first published in August 2004

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