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Data Replication for a Disaster Recovery

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Radoslaw Czajkowski
January 19, 2007

Radoslaw Czajkowski
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IT requirements concerning a disaster recovery are usually quite complex but if you take your time and create a disaster recovery plan then implementing these solutions will be easy and will let you be well prepared in case of an eventual disaster.

Nowadays there are a lot of companies that can help you in preparing a disaster recovery plan and train your employees how to quickly get back to business after a disaster happens. Not every company however opts for this kind of solution. Many of them just don’t want outside people to look at their business. It may also be quite challenging when other people tell you that your solution doesn’t work and needs changes.

Most if not all of the companies these days require a good backup solution that provides a copy of the critical business data. Companies also would like to have a guarantee that all the data the business has will be recovered in case of a disaster.

Therefore to provide companies with their needs there are several solutions available that will make the data safe and easy to recover.

The most common disaster recovery solutions that companies use nowadays are:

1. Mirroring – this solution creates an exact copy of your existing data. To provide a good recovery solution this requires a separate disk on which the original data will be stored. You would also want this separate disk to be in a different location than the original data. Having your backup disk in a different location also requires high bandwidth connection between two locations.

2. Host-Based Replication – this kind of replication resides on the server that needs to have its data backed up. This solution has an advantage that the cost can be very low. However depending on how many servers the company has this cost can go up and can be significant. The downside is that it is a decentralized solution and most of today’s companies trend toward centralization. The other disadvantage is that using host-based replication has impact on host’s CPU, memory and network. There are many cases that this disaster recovery solution fits in. It may be used for example for a low-cost disaster recovery protection of file servers and print servers the company has or protecting key applications the company runs.

3. Appliance-based replication – appliance is a dedicated hardware and software system designed for solving a specified task. In this case the appliance is designed for performing all replication tasks and resides between the host and the storage. The advantage is that there is no impact on host’s CPU and the host even doesn’t know that there is the appliance that takes care of backing the data up. The downside is that the appliance itself may become a bottleneck if there are a lot of hosts needing replication services.

4. Storage-based replication – This kind of replication is a combination of host-based and appliance-based solutions. There is no overhead on servers and a replication takes place without them ever knowing. The other benefit is that the management is centralized and any server that the storage system supports can utilize replication features of the storage device. The company may also use solutions provided by disaster recovery vendors which use their own proprietary software and provide the company with a constant monitoring.

All these data recovery solutions have advantages and disadvantages. The solution which your company will use is dependent on several different factors. Of which the most important are: the size of your company, how critical your data is and how much money your company spends on a disaster recovery.

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