How disk has changed backup


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However, the value of stacking in most open-systems environments is questionable because any decent backup product can append to a tape until it's full. You should be aware that the use of stacking breaks the relationship between the backup software's media manager and the physical tape. Products that support stacking must read the entire stacked tape to read just one of the virtual tapes included on that tape. This feature is useful only if you gain a benefit akin to that achieved in the mainframe environment.

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Alexander Dubose Jones and Townsend LLP, a small appellate law firm with offices in Houston and Austin, Texas, moved from tape to LiveVault Corp.'s InSync (Live- Vault service), a continuous data protection product. Vicki McArthur, the firm's administrator, says they had previously relied on daily tape backup as well as on a seven- day offsite tape rotation. The firm experienced all of the challenges traditionally found in tape environments, but recoveries concerned McArthur the most. Nightly backups don't work well with the nature of the legal industry, where files often require last-minute changes. Under a traditional backup system, files created in the morning wouldn't get backed up until that night, and wouldn't be sent offsite until at least the next day. "We faced the possibility of losing an entire day's worth of work or worse," says McArthur.

LiveVault makes a backup of files as soon as they're saved, and then replicates them to a remote site within a few minutes, where all previous versions of any file are accessible at any time. Because only changed bytes are sent, very little bandwidth is required. And since data is replicated every 15 minutes, McArthur believes that "the amount of data loss due to user error is reduced to minutes, possibly less."

You also need to think about which type of notification the VTL supports, especially if you're considering an integrated VTL. Some support SNMP traps, a few support e-mail notification, while others require a storage admin to log into a Web page to be notified of any issues.

If high-end performance is important, you should look for a VTL with a multiple data-mover architecture. Most VTLs run all software on one VTL head. Some vendors use the VTL head as a control mechanism, while passing the movement of the data on to one or more data movers. Need more performance? Simply purchase more data movers. This allows scaling to a much higher level without having to add and administer another VTL (Diligent, Neartek and Sepaton use this approach).

Finally, remember that VTLs don't perform at the same level, so it's important to conduct performance testing in your environment.

Alternative backup methods
If you have a centralized data center with a four-hour recovery time objective (RTO), a 24-hour recovery point objective (RPO), a 24-hour synchronicity requirement and an eight-hour backup window, you can stop reading now. But if your backup requirements include remote, unattended data centers, a five-minute RTO, a 15-minute RPO or a non-existent backup window, alternative backup systems can help bring some needed sanity to your storage environment.

Alternative backup options include snapshots, replication, continuous data protection (CDP) and data reduction backup (DRB). These technologies will reduce backup and restore times, and help meet requirements such as RTO, RPO, backup window and synchronicity.

RTO--how long it takes to recover a system--can range from zero seconds to several days or even weeks. Each piece of information serves a business function, so the question is how long the business can live without that function. If the business can't live without it for one second, then the RTO is zero.

RPO is determined by how much data a business can afford to lose. If the business can lose three days' worth of a set of data, then the RPO is three days. If the data is real-time transactions essential to the business, the RPO is zero for that application.

There can also be an RPO for a group of machines. If several systems are related to each other, they may need to be recovered to the same point in time. This is the synchronicity requirement; to meet it, all related systems have to be backed up at exactly the same time. This is referred to in disaster recovery circles as consistency groups.

This was first published in November 2005

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