Blade servers for vm?

Blade Centres are a way of achieving a high density of computer power in a small, well defined and contained unit. Other than their ability to reduce cabling mess, power drain, space requirements, etc. compared to traditional 1U servers, there's nothing special about them; each blade is a seperate server and you still need to plan how to provision, manage, etc. each blade (though some high end blade centres will come with tools to make this easier, too...).

They have potential disadvantages too; a blade centre with just a few blades might cost more than a number of equally configured 1U servers, they generally can't carry massive local storage on each blade, and network/comms might be an issue, both in terms of number of ports available and flexability of configuration.

Having said that, we use Dell's current Blade offerings for some of our ESXi servers and we've been very pleased with them, and I know plenty of other places that are using blades from other vendors equally happily.

Different vendors sell different types of Blades, so the answers depend on the type of blade system that you get. HP BladeSystem is one popular kind of blade.

is the whole enclosure seen as one big machine and yhr more blades you add the more computing power/resources you get in VMware - or are the just x number of seperate servers?

Each blade is it's own server. Each blade has it's own CPU, Memory, usually have their own harddrives and remote access, etc. The blades plug into a blade chassis, and the chassis handles power & cooling. Networking tends to be handled on both the blade and the chassis.

Remote access exists on each blade via something like IPMI or iLO ("Integrated Lights Out"), but the chassis tends to have a management interface which organizes the iLO interfaces.

The chassis handles interconnects, the switching layer, and perhaps does some routing. The power cables, network cables, keyboard/video/mouse, etc. are plugged into the chassis.

Think of blades like two dozen small servers inside of a single chassis.

VMWare can be installed just as it can on a traditional rackmount server. ESXi can be installed to the local disks, or can be loaded from a SD card or USB stick (disks are never touched), loaded from the network, etc.

Well, a Blade CENTER is a cage for blades which are indicvidual servers. They share some hardare (power supplies, central routing, controller subsystem and KVM) but at the end every BLADE is a SERVER. The advanttage is central administration. The negative is the price for the center / chassis.

Whether it makes sense for you is - your decision. I tried to lik ethem, I realized they are stupidly expensive. SuperMicro has "Twi" cages with special mobos that are 2 servers HU and possibly cheaper (at least for me).

The setup of using Blade Servers and VMs is great, dependent on your budget.

Especially when you combine that with SAN storage. The individual blades themselves would be the ESX hosts (Cluster them), and you would have shared SAN storage (iSCSI, virtual iSCSI, etc) that all the ESX hosts could store the VMs on. Then blade enclosure acts as centrialized management for all the physical blades and the uplink(s) into the physical network.

If your ESX hosts are clustered, you can take advantage of some HA features that will automatically migrate your VMs to a new ESX blade if you have issues with another. Additionally, when clustered, VMs can be distributed across ESX servers based of resources usage (automatically, or with policies). Another benefit of having a setup like this, is you can utilize SAN replication to backup your VMs.

Keep in mind these additional ESX features require vCenter and Licensing.