Q

Should I use two non-synchronized/distinctive servers for redundancy?

Is using two-non synchronized servers the best way to achieve redundancy in the data center? Expert James Geis gives his opinion in this expert response.

Would you consider the use of two non-synchronized/distinctive servers an efficient means to provide redundancy? I have a vendor who claims that such a configuration represents most optimal solution. As far as I can see, it causes an administrative nightmare. It adds field equipment.

My short answer would be no. This is a common question with uncommon answers, depending on the vendor and their

solution. The available solutions to server synchronization have become more complex, as a clustered configuration is no longer the only option. Servers can be replicated by a myriad of tools now—via the operating system, third party applications or even via networked storage arrays.

Synchronization via the storage array coupled with virtualization software is your better option. One of the advantages to using virtualization is that you can have heterogeneous hardware (different configurations, different CPUs, different storage arrays, and even different manufacturers) on both the target and source, as long as the virtualization software can "see" the storage that contains the operating system image. You can replicate the server image via virtualization software that works in sync with networked storage arrays.

Note that this approach does have pros and cons. Due to the dependencies from the transaction intensity of the operating system and resident applications (higher I/O means more storage replication cycles), this will impact the network, especially for long distance replication. Storage must be replicated more frequently the more changes to data, or the more business-critical operations an application has. This requires some forethought into LUN planning for storage and backup; you'll need to make the decision between large versus small LUNs, and whether you back the machines up through the virtual machine or the storage array.

This was first published in September 2007

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