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Many people think about blades as the best way to put many small servers in a small amount of space. Often this is the case, but not in every case. Last weekend i did some research for a project and found out something interesting in the offering of our competitor HP.

Let´s assume you have the requirement to use a quad processor blade. So you need one of the full height blades of HP the two disks of the blade aren´t sufficent your you. You need more of them. Our beloved competitor has a blade shelf for this. It´s called HP StorageWorks SB40c storage blade. It´s a half height blade.

Okay, let´s calculate a little bit. You could put 16 half height blades and 8 full heigt blades into a 10 rack units c7000 blade enclosure. Okay, we need some bays for the storage. You would assume that you can put 5 full height blades into the system and 5 storage blades in the free remaning bays (leaving one free) into the system, but this isn´t the case. The storage blades have to be adjactent to the blade. More important, you can put it only in the lower bay.

A half-height SB40c storage blade must be installed within the same partition as its partner server
blade. If the SB40c is partnered with a full-height server blade, the SB40c must be installed in the
lower bay adjacent to the full-height server blade. The HP BladeSystem Enclosure Tech Brief states:

You could put a server into the free bay above the storage bay but there is an interesting gem in the documentation. The quick spec document states at the HP website states:

NOTE: The lower tape or storage blade cannot be removed without first removing the upper half height blade.

The problem, as far as i understand the datasheet of the SB40c it isn´t just a bunch of cabling. It has an own RAID-Controller( HP Smart Array P400 with 256MB Battery Backed-Write Cache). It´s an active component and there is some likelihood that active components will fail, especially when they contain batteries.

Let´s assume you have used the slot above the Storageblade for another system. Let´s assume you have to service the storage blade. You have to shut down the perfectly running system on the blade above the storage blade, as you have to remove it first. Doesn´t sound reasonable for enterprise usage. This leads me to the conclusion that you you use the c7000 enclosure only for 4 full height quad socket blades with 4 storage blades and nothing else.

Okay, that implies that you need 10 rack units (the size of the c7000 enclosure) to implement 4 quad socket systems with 3-8 disks with the HP blades. Now let´s look at the problem from a different perspective: The Sun Fire X4450 is a quad socket socket server with up to 8 harddisks (with more PCIe-slots than a blade). The system takes rack units in you rack. So you could place 5 of them at 10 Rack units. Sometimes the denser solution is at a place where you don´t expect it.