Dissecting Virtual Tape Libraries
Bryan J. Smith
For a company that will never have a data loss event, backup is optional.
For companies that will experience a data loss event, recovery is not optional.
So, invariably, backup of any and all data that may need to be recovered is
not optional. Backup strategies are still widely debated, with many beginning
to claim tape is a legacy solution that can and should be completely replaced
by disk. Keeping recovery clearly in mind, while disk may solve many backup-time
issues, disk still has serious environmental, longevity, and portability issues.
The focal point for the debate does not begin with media/medium. Given advancements
in both operating system and networking technologies over the past decade, all
recovery strategies now basically fall into three main categories:
- Online -- Transparent solutions such as redundant array of independent
disk (RAID) storage and system clustering/failover, as well as the availability
of filesystem snapshots.
- Off-line -- System storage or removable media for both short-term and long-term
recovery needs. Traditionally, this is removable tape cartridge and, increasingly,
both fixed and removable disk.
- Remote -- An online variant, mirror data to systems on a remote network
(typically over the Internet).
Online recovery is still at the mercy of filesystem corruption, let alone
physical disaster, which negates RAID, clustering, and snapshots. Remote backup
solves the physical disaster issue, but bandwidth is proportional with cost,
which results in most remote backups being only a subset required for nominal
operation. So, while both newer online and remote recovery solutions are a welcome
supplement to the traditional, off-line recovery procedures, they can only augment
off-line recovery, not replace it.
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