How many Raspberry Pi clusters need to achieve the same performance as the server?

I want to build a Raspberry Pi cluster to serve as the front-end of the website. The website is written in php without a database. I want to know how many Raspberry Pi is required to achieve the same performance as an E3 server (or other pc servers). has anyone done a similar test? I want to build a Raspberry Pi cluster to serve as the front-end of the website. The website is written in php without a database.
I want to know how many Raspberry Pi is required to achieve the same performance as an E3 server (or other pc servers). has anyone done a similar test? Reply: First of all, let's use an idealized trick to calculate the economic account. someone on the internet has done a Linpack Benchmark Results test on the floating point performance between Raspberry Pi and several table-level CPUs. ), Paste the following results:
PC:

Double Precision 100x100 compiled at 32 bits                              Opt    No optCPU                 MHz    MFLOPS    MFLOPSCeleron C2 M       2000   1092.56    121.25Core 2 Duo 1 CP    2400   1315.42    195.13Phenom II          3000   1412.83    244.43Core i7 930        ****   1764.75    428.00Core i7 860        ####   2004.31    381.97Core i7 3930K      &&&&   2529.73    746.01Core i7 4820K      $$$1   2671.15    892.04Core i7 4820K      $$$2   2684.05    895.54Core i7 3930K      OC     3112.94    926.92

Raspberry Pi is not suitable for high-performance environments in terms of design. but in another scenario, it is still promising to use the arm-based server solution.

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1. Raspberry Pi 2 B Cluster

On Weibo, the original po was called Deng grassland.

If it is floating point computing, Raspberry Pi will fail
I/O throughput for Raspberry Pi is promising.
We have used cubieboard for test and learning. The performance of Raspberry Pi is not as good as it promotes when the cost is limited. my own test result is: Raspberry Pi runs a phpinfo, I can feel the obvious delay, and on my old Android phone, the memory is also mb, running wordpress is very smooth.
It seems that the cpu frequency and disk I/o are hard. TF card is really not getting up. The cluster has the advantage of processing a large number of operations. Simple http requests do not show clusters, but become slower. Not as fast as a Raspberry Pi. Compared with floating point performance, it is not a supercomputer.

I want to achieve the same performance, but I have nothing to do with it-rPi's IO performance is too bad.