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linuxshelldiskhard-drivedd
Amir
Amir

Reputation: 6186

Disk Throughput - new file vs. existing file using dd

I wanted to measure my disk throughput using the following command:

dd if=/dev/zero of=/mydir/junkfile bs=4k count=125000

If the junkfile exists, my disk throughput is 6 times smaller than if junkfile does not exist. I have repeated that many times and the results hold. Anybody knows why?

Thanks,

Amir.

Upvotes: 4

Views: 317

Answers (1)

Eric Fortis
Eric Fortis

Reputation: 17350

In order to minimize disk caching, you need to copy an amount significantly larger than the amount of memory in your system. 2X the amount of RAM in your server is a useful amount.

from http://www.westnet.com/~gsmith/content/postgresql/pg-disktesting.htm

Upvotes: 3

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