While the majority of the internal and external systems use 3.5-inch drives, HP has lead the path to 2.5-inch drives through its server and storage offerings. Some would argue that the lower cost per GB is the reason why the 3.5-inch drives have remained so popular; others would point to the capacity gap - 2.5-inch drives offer about half the capacity of 3.5-inch drives. However, there's a growing number of people who have realized the energy costs need to be considered as well as the acquisition cost per GB.
IDC discusses the capacity gap, the cost to power and cool storage, as well as the industry transition to 2.5-inch drives in a whitepaper available at: http://h18004.www1.hp.com/products/servers/prolian
In the paper, IDC states:
The 2.5inch SFF performance-optimized HDD is already well-recognized for providing greater storage density and higher IOPS per U in server and storage systems as well as consuming less power. But a 2.5inch form factor HDD carries a capacity penalty of roughly half that of a similar-generation 3.5inch HDD. The reason is simple: 3.5inch HDDs can have a maximum of four platters per drive, while current performance optimized 2.5inch HDDs have a maximum of two platters per drive. However, this is not a fixed rule, and HDD configurations are about to change.
IDC goes on to predict that "the HDD industry's last generation of 3.5inch performance-optimized HDDs will be launched in 2009."
Do you agree that the server and storage industry will transition to 2.5-inch drives faster than before?