How disk has changed backup


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Kelly Overgaard, systems manager at Adaptec Inc., was fed up with tape. "Our old system was at capacity, and something was always breaking," he says. "When we looked at disk-based solutions, our goal was to completely get rid of tape--especially for remote sites."

Adaptec chose an Avamar Technologies Inc. Axion system that uses "commonality factoring" to identify duplicate blocks of data throughout its enterprise and to transmit only the new, unique blocks of data each time it backs up. This allows Adaptec to back up and recover smaller remote offices directly to its central data center. Larger offices, or those with shorter recovery time objectives, can be backed up to a local target device at the remote site, which then replicates to a second device in its central data center. This flexibility to use (or not use) a local recovery device let Adaptec deploy this solution to several sites.

Overgaard says that because the commonality factoring is performed on the client, it requires slightly more CPU than traditional backup, but "no one has mentioned any ill effects." He considers himself a happy customer, but says he's unsure if the system will be able to back up Adaptec's large databases.

But Overgaard doesn't believe he can afford to store his firm's backups with long-term retention on the Axion system, so he also performs a monthly full tape backup of Axion clients using Adaptec's previous tape system, and then sends that offsite for several years. Avamar says he'll soon be able to make such tape backups by simply exporting the appropriate data directly from the Axion system.

When used with snapshots, replication requires only tiny backup windows. The snapshot takes just seconds to create, and replication is the quickest way to back up that snapshot to another device. You can also cascade replication to provide multiple copies, such as an onsite and offsite copy. If you want to provide a tape copy of the replicated snapshot, just back up one of the destination devices. But replication software doesn't usually provide recovery features. The RTO, RPO and synchronicity requirements that you'll be able to meet will be based on how you're performing snapshots or backups, and how quickly they'll be able to recover.

DRB SYSTEMS. DRB systems were designed to answer the following questions: If only a few bytes in a file change, why back up the entire file? If the same file resides in two places on the same system, why back it up twice? Why not store a reference to the second file? And why waste server and network resources by backing up the same file across multiple systems?

By backing up a file once, and then backing up only the changed bytes, backup windows are reduced. Tape copies of disk-based backups can usually be created at any time, depending on your requirements. Some DRB products can meet aggressive RTO requirements by restoring only the blocks that have changed since the file was last backed up. The RPO and synchronicity abilities of DRB products are based on how often you back up, but it's common to back up hourly.

The biggest advantage to DRB products is that, from the user adoption perspective, they're the closest to what users know. Their interfaces are similar and they often have database agents like traditional backup software. They're also able to back up faster and more often, and use much less bandwidth.

This was first published in November 2005

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