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I am disappointed with the unreliable disk I/O in VPS (no matter what the virtualization and cpu/ram specs, shared disk often becomes a bottleneck).

Can someone tell me whether the disk in cloud hosting is shared? For example, if I go for Amazon EC2, is it more like an on demand VPS with shared disk/ram (on a huge box) or like an on-demand dedicated server.

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3 Answers

Amazon EC2 and cloud are on demand VPSes with shared disk and RAM but the providers allocates fixed amount of resources to your instance. A VPS can almost never measure up to the performance of a dedicated server.

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Pretty wrong. A dedicated server and a smaller vps is ruinning on server storage. I bet amazon runs a hugh san ni the backend wihch shares the io load. I know people getting 100mb/s runnning loads with random io on amazon. –  TomTom Jan 26 '11 at 17:24
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As Sameer mentioned earlier that in cloud IaaS you get access to shared resources, but for CPU, HDD-space, RAM you get a guarantee. However it is also important to note that AWS (& other IaaS providers, I'd imagine) provide different options where the no. of processors, amount of RAM, and I/O performance can be light, moderate or extensive. Apparently some providers allow you to mix-n-match cloud-hosting and colo.

It is a commonly held belief that in cloud service s.a. AWS, to make the best use of their infrastructure, you may require a completely re-architected/redesigned system, which leverages the strengths of cloud infrastructure. Take the google live-search feature for instance, or Youtube for that matter. I am sure you'd agree that these are pretty i/o intensive usage of cloud infrastructure. Of course, we may not have he luxury of doing so, always or immediately.

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"Unreliable"? do you mean as in "the performance varies" or as in "sometimes it's just not there"? I can see why a cheap VPS/Cloud/whatever service might have variable IO performance but it shouldn't be disappearing etc. Certainly there's nothing inherently unstable in any hypervisor - if they're cutting corners or being incompetent then that's a different matter.

As for the IO model of cloud computing, well it varies, there's hundreds of companies doing this and they all use different components and setup/manage them differently. Even with EC2 they won't use a single storage model, the basic API is obviously the same but some of their subsystems will use one storage vendor/connection/disk-type etc. while elsewhere it'll be different.

If you have specific requirements why not come back to us with them.

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