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In which cases do you think that a Blade is better than a rackmount, in a virtualization environment?

If you think that blades are much better than Rack, then why facebook prefers rackmount?

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closed as not constructive by ewwhite, Shane Madden, MDMarra, Zypher Nov 12 '11 at 8:43

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In many ways what is bests depends heavily on things external to the equipment. How much does your space cost, how expensive is your power and cooling? – Zoredache Nov 12 '11 at 2:58
up vote 2 down vote accepted

Blades can cram some incredibly dense computing power into a rack.

Let's say you configure an 8-blade chassis, and each blade is identical:

  • 4x 12-Core Opterons
  • 256Gb RAM

That's 384 cores and 2TB of RAM in about 10RU. Your power consumption is going to also be pretty good (all things considered), and you get really, really cheap and fast interconnects between the devices in the same chassis (We have specced two Dell M910 blades similar to above, and they have 4x 10GbE connection along with 8x 1GbE for each blade).

But you need to have the budget to support it, as that configuration has no storage, and is going to cost substantially more than populating the 8x 4U servers you would usually need for that sort of configuration.

Additionally, I feel that blades are reall only just touching the edges of "commodity hardware", because although they're "normal" servers, they are far from normal in terms how they are configured and deployed, and you can not mix and match.

I can't speak for Facebook obviously, but my guess is that:

  • They're not short on space (I've seen the photos of their new DC, it's massive)
  • Like Google, they see the value in commodity hardware
  • They're after the best value for money

Blades are generally not value for money, but they are great when you're short on space.

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The requirements of the situation dictate which option will be most appropriate. There is no fast and easy rule or everyone would use the one server that perfectly met those needs. The following comparisons are highly generic, and are not true of all specific examples of server equipment.

  • Blades are the most expensive, but smaller and have superior connectivity and management.
  • Rackmount are cheaper, and are a good balance of manageability, density, and cost.
  • Tower are the cheapest, and have the worst management, both logical and physical.
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This is not a very well researched and posed question. There is no "better than". There are only your or your customer's requirements, which could be met by either rack-mount or blade servers, depending on the details.

You talk about "a virtualization environment", which is a pretty useless statement without specifics. The following is a non-exhaustive list of questions to which you should know the answers before you can decide if you need blades or if rack-mounted servers fit your needs: Do you have a centralized storage solution? Is it highly available? What are your storage needs in general and how do you expect they will change over time? How many virtual machines will there be? How is their number expected to grow? What kind of workload will there be? How will you manage the virtual machines, network and servers? How does your network look like? How many members in your admin team? What is each member's level of expertise? Do you colocate or do you run your own server rooms? How stable is the energy supply? All this and more needs to be taken into consideration when designing a "virtualization environment".

Blade servers usually have very limited storage capacity and only few (usually two) network interfaces, so a SAN solution and all it entails is practically mandatory. Blade systems are also very expensive to fully equip (network/fabric switches, power supplies, additional network interfaces and HBAs and component redundancy in general) but if you regularly and/or quickly need to add more processing power to the installation it is much easier and quicker to insert a new blade server than to mount, connect and wire a new rack-mount server. This, along with the high resource density and fast interconnects they allow for, is basically the number one reason for blade systems. The integrated management tools most blade systems have also make it easy to access and configure blade servers and switches in a centralised manner, which can also save manpower.

In many cases, however, well-equipped, high-end rack-mount servers will do just as well or even better at lower costs. Of course you need the infrastructure to support that, much of which a blade system already provides by itself (network, power, wires, ...).

There is no easy answer and it all depends on your requirements, but when you are not sure if you need a blade system, you probably don't.

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The blade enclosures I use are 10U high and hold up to 16/32 blades, the blades I buy are pretty close functionally to the 2U high 'pizza box' servers I sometimes buy, so for me if I need 5 or more servers in a rack and don't need more that 2 PCIe slots then I buy blades as that's the break-even point per rack, otherwise I buy 'pizza boxes'.

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