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What are the advantages and disadvantages of clustering low-end servers over single high-end server?

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5 Answers 5

up vote 3 down vote accepted

Cluster

  • Fewer single points of hardware failure.
  • There are cohesion overheads incurred tying everything together.
  • You need configuration management of some form, however basic/manual.
  • Depending on configuration can be physically smaller/larger, need more/less power and - require more/less cooling.
  • More LAN/SAN/power ports required.
  • May need some form of KVM.
  • May use lower quality components.
  • More things to monitor.
  • Upgrades/updates can be harder.
  • Server downtime can be arranged without service impact.

Single Bigger Box

  • System board is usually a single point of failure.
  • No cohesion overheads or config management needed.
  • Depending on configuration can be physically smaller/larger, need more/less power and - require more/less cooling.
  • Less LAN/SAN/power ports required.
  • No need for a KVM.
  • Often higher quality components.
  • Less things to monitor - though you often get more sensors that you CAN monitor.
  • Upgrades/updates can be easier.
  • Server downtime is always service impacting.

It's this last item that matters most to me, and why I never buy a single box for production systems.

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It depends on your goals and workload, it really really does.

If you're just going for high-availability, multiple servers is better than a single big server. The multiple servers can be mid class, or even low class depending on whether or not the cluster's services can be broken up, and how well they take to load-balancing.

If you're looking for computational resources, not all workloads parallelize well and those would be better served by a big machine with a few fast processors. Other workloads parallelize very well, and those would be served by multiple machines. Whether or not the multiple machines are netbook class performance machines or mid-range servers again depends on what you want to do with them and how fast you want to get there.

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Cluster of low-end servers:

  • +: Redundancy
  • -: More configuration/management

Single high-end server:

  • +: Easier to configure/manage
  • -: Single point of failure. You can reduce this risk by adding redundancy inside the server (e.g.: using RAID for your hard-drives)
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It depends on many things; primarily, what do you need the server(s) for, and what exactly do you mean by 'low end'? But just some junk to throw out there:

One High-End server Disadvantages:

  • single point of hardware failure (lack of redundancy)

Cluster Disadvantages:

  • can be more expensive in total
  • wasted resources vs. Virtualizing a single server
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Could you explain "wasted resources"? Thanks. I want my applications to be distributed; seeking for disadvantages. –  Jeff Nov 23 '10 at 18:51

Can you give us detail about what you are trying to do? Are you clustering Windows, Linux, vmWare, Xen? What is you application: web servers, Database servers, email servers, etc.

An advantage of low-end over high-end is distributed resources and easy replacement but is there enough power for the service you are providing? I can't tell with the info you have given.

A disadvantage with low-end would be a requirement for better operational conops and potentially more staff if you deployed a lot of smaller hosts.

If you are virtuallizing you may want big machines to host your ESX/Xen/Hyper-V and then cluster them, with additional clustering at the OS level.

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Distributed web application with low storage and computation needs. Clustering fits my needs, but I have a fear of wasting sources. –  Jeff Nov 23 '10 at 17:50
    
Are you using a load balancer or other kind of front end? Properly balanced web apps are good candidates for low-end servers. You will need to invest in the backend database and have the increased cost of the load balancer. In other words I would spend my funds on the load balancer and save on the web servers. –  Tom Seibert Nov 24 '10 at 14:19

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