Disaster Recovery Extra: 10 hidden perils of DR planning


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5. The DR plan specifies only system RTOs, not data center RTOs.

Most companies that have negotiated RTOs have negotiated these numbers for individual systems. For example, a common RTO is that any system in the data center must be recovered within four hours. While this works fine for operational recoveries and system-level outages, it doesn't work when the entire data center is lost. It's usually assumed that a system that needs to be recovered is given access to all system resources. For example, a large database server that needs to be recovered is given access to all 20 tape drives in the tape library. But what happens when 20 or 100 servers need to be recovered? They can't all be given access to all 20 tape drives in the tape library.

This is quite possibly the most difficult conversation that needs to occur between IT and those business units that need a DR plan. It brings to light one of the core problems with traditional backup and recovery: In a true disaster, it's fairly certain that the storage department isn't going to meet its RTOs or RPOs. Unless your company is able to live without its data for several days, the only way to have an entire data center's data available after a disaster is if it was "recovered" before the disaster happened. Traditionally, this has been accomplished with replication. Depending on the amount of data, it can also be accomplished with other technologies. But realistically, the working RPOs

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and RTOs of most companies don't allow the recovery of an entire data center to begin after a disaster.

6. The DR plan doesn't contain consistency groups.

Multiple computer systems often serve multiple business applications. The systems need to be restored to the same point in time. But typically, this is another area where there's a mismatch between the needs of the business and IT's capabilities. Unless consistency groups (a consistency group is a collection of volumes across multiple storage units that are managed together when creating consistent copies of data) have been created, it's highly unlikely that there's technology in place to recover a group of systems to a single point in time. This is another dirty secret about the way most backup systems work. It's not possible to create a consistency group without advanced technology such as snapshots, replication or a continuous data protection system.

This was first published in May 2006

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