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Preparing for a disaster is more often than not part of the storage planning process, and without question, it is one of the most difficult tasks, since it includes local hardware and software, networking equipment, and a test plan to ensure that you can recover from the disaster.
There are four questions you should ask to determine your disaster recovery requirements. They are:
- How soon after a disaster do I need to be back up?
- How much data has to move back and forth daily?
- How far away is the disaster recovery site?
- What am I doing with my data now (HSM/backup)?
Replication of data is the biggest issue. You have two types of data (disk-based and HSM-based tape issues), and each has its own complications. In this article, we will cover disk-based disaster recovery, and next time review the issues surrounding replication of HSM data over long distances.
Anyone trying to develop a disaster recover facility must replicate data. Up until the last ten years or so, data replication was often done with sneaker net (for those of you not old enough to remember, that's running the data to the other site, usually on tape). Since that time, networks have gotten faster and cheaper, and software has been developed to take advantage of these networks, both on the RAID and host side.
Data replication has two major components. The first is the method of replicating the data at the other site, usually either host-based replication or storage-based mirroring technology. The other issue is how to transport the data to the other site, either via WAN and IP or dark fiber and a Fibre Channel connection.
The technologies and products associated with each should be carefully considered, since changing disaster recovery plans and methods is not easy and certainly not cheap.