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I am testing disk I/O performance on a server of mine, which will eventually run Postgresql. I am following this web site to perform my benchmarks.

The benchmark consists of running dd and reading/writing N blocks the size of 8k (which is the size of blocks Postgresql uses). N is to be calculated as follows:

N = 250,000 * gigabytes of RAM 

So, I have 16GB of ram, which gives me 4 million blocks to read/write. That is fine, but...

I am unsure where the magical number of 250,000 comes from?

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up vote 0 down vote accepted

Edit: Corrected per Eviler_Elf:

That's for converting between blocks and GB:

 1 GB / 8 kB/block * 2x = 250,000 blocks
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ok thanks but for clarification: 1 GB / 8kb/block = 125,000 blocks, but in the article, he says to use 2X the amount, which gets you to 250,000 – Eviler_Elf Nov 17 '11 at 20:14
@Eviler_Elf good catch. I should have been a little more careful writing up my answer... – gsiems Nov 17 '11 at 22:32

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