Wednesday, January 5, 2011

Are cloud storage providers good for primary data storage?

Why not use a cloud storage provider?
The most persuasive argument against using cloud storage for primary storage is application performance. Application performance is highly sensitive to storage response times. The longer it takes for the application's storage to respond to a read or write request, the slower that application performs. 


Public cloud storage by definition resides in a location geographically distant from your physical storage when measured in cable distance. Response time for an application is measured in round-trip time (RTT). There are numerous factors that add to that RTT. One is speed of light latency, which there is no getting around today. Another is TCP/IP latency. Then there is a little thing called packet loss that can really gum up response time because of retransmissions. It is easy to see that for the vast amount of SMB(small mid sized business) primary applications, public cloud storage performance will be unacceptable. 


When do cloud storage services make sense?
If an SMB is using cloud computing services such as Google Docs, Microsoft Office 365, or SalesForce.com, then it makes sense to store the data from those apps in a cloud storage service. In those cases, the data storage is collocated with the applications. Response time between the application and storage is the same as if the application and storage were in the SMB's location. The key issue here is the response time between the cloud application and the SMB user. In this scenario, the collocated storage is not the bottleneck to user response time. Therefore, if the cloud application performance is adequate, so too is the cloud storage.
If the cloud storage and the application that's using it are collocated, then it makes sense to use cloud storage as SMB primary storage. Otherwise, slow application performance would make using a cloud data storage provider a poor choice for your SMB environment.

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