New backup strategies


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Pros and cons of alternative backup methods

Setting RPO, RTO requirements
All RPO, RTO and synchronicity requirements must be business-centric. Before deciding what these requirements are, you should first analyze and prioritize the business functions, and assign each computer system the recovery priority of the

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business function it serves. Next, decide on an RTO and RPO for each system and type of disaster--from the loss of a disk to the loss of a metropolitan area. Some systems will have the same requirements for all types of disasters; others may have tougher requirements for specific types of disasters.

Once you've determined an RTO and RPO for each system and disaster type, the final step is to determine how long it will take to back up the system and how much the backup will impact the production system.

Everything should start with RTO and RPO, although very few people do it that way. Most people go right to the backup window. Instead, you should concentrate on meeting your RTO and RPO requirements and the backup window will almost always fall right in line. The reverse isn't necessarily true, however. There are many things that will shrink your backup window but not help your recovery objectives. If your requirements are impossible to meet with a traditional backup system, the following technologies are worth considering.

Snapshots. The most common type of snapshot is a virtual copy of an original volume or file system. The reliance on the original volume is why snapshots must be backed up to provide recovery from physical failures (see Match snaps to apps). Snapshot functionality resides in a number of places, including advanced file systems, volume managers, enterprise arrays, NAS filers and backup software.

Snapshots can help you to meet aggressive backup requirements. For example, some snapshots can meet an RTO of a few seconds by simply changing a pointer. An aggressive RPO can be achieved by creating several snapshots per day and, because snapshots can be created in seconds, you can also meet stringent backup window requirements. For instance, it's possible to create a stable, virtual backup of a multiterabyte database in seconds--reducing the impact on the application to potentially nothing--which leaves hours to perform a backup of that snapshot. The next section discusses how replication is a great way to do that. Finally, creating synchronized snapshots on multiple systems is also fairly easy.

Adaptec switches from tape to disk
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.

In addition, 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.

There's a growing list of APIs that allow different vendors' products to interface with snapshots; the network data management protocol (NDMP) and Microsoft Corp.'s Volume Shadow Copy Service (VSS) are examples. NDMP lets backup products create a snapshot, and catalog and restore from its contents. VSS allows storage vendors with snapshot capability to have the files in those snapshots listed in and restored from the Previous Versions tab in Windows Server 2003. Hopefully, this capability will be added to workstation versions of Windows and more NAS vendors will support VSS.

Another interesting development is the creation of database agents that work with snapshots. The database agent communicates with the database so that the database believes it's being backed up, when all that's really happening is the creation of a snapshot. Recoveries can be incredibly fast when the process is controlled by the database application.

Replication. Replication is the practice of continually copying from a source system to a target system all files or blocks that have changed on the source system. Replication used to be what companies implemented after everything was completely backed up and redundant, which meant that few used replication. However, many people are now using replication as their first line of defense for providing backup and disaster recovery.

Replication by itself is not a good backup strategy; it copies everything, including viruses and file deletions. Therefore, a replication-based backup system must be able to provide a history by either occasionally backing up the replicated destination or through the use of snapshots. It's usually preferable to make a snapshot on the source and replicate that snapshot to the destination. That way, you can prepare database applications for backup, take a snapshot and then have that snapshot replicated.

When used with snapshots, replication allows for 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.

This was first published in June 2005

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