I attended the Server Blade Summit last week. While the show focused more on the adoption of Virtual Machine technology (VMWare, Xen, etc) in the data center than on blade servers, some interesting trends regarding SAN attach rates for blade servers emerged.

In non-blade server world, the SAN attach rate (HBAs in servers) is somewhere around 15%. In blade servers, where direct attached storage is limited, the attach rate approaches 40%. And when VMs are added to the picture, the attach rate soars to near 80%.

Why is this? Virtual Machines are location independent. A VM can be suspended, put on the shelf and restored days or weeks later. And when a VM is restored, it can be restored on any processor blade in the complex. This requires that the storage associated with a VM be able to follow the VM to different processor blades. A perfect application for SANs and a driver behind the much higher attach rates for blade servers with VMs.

About the numbers- The 15% and 40% numbers come from conversations with IBM and HP. The 80% number came from a presentation I saw at the Server Blade Summit. If anyone saw the presentation and can properly attribute the numbers, please send me a note.