About Linux under DD Test disk PIT!!

In Linux you want to know the disk read and write speed, the database can withstand much pressure is also very helpful. There are many ways to do this. But what I'm going to say today is about DD.

A. With regard to the readings

Time DD If=/dev/zero of=/var/test bs=2m count=3000

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Wow, so fast speed, I can't believe my eyes. If you do not know the configuration of the server, I think it is really so fast!!

B. Test and write again.

Time DD if=/var/test Of=/dev/null bs=2m

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Don't believe in your own eyes.

C. Another one.

Time DD If=/dev/vda3 of=/var/2017 bs=2m count=300

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The same is a machine, why the difference is so big??

Let's take a look at what each parameter means.

Detailed command:
Time for timing (real time-consuming, user-state time-consuming, SYS system-state elapsed)
DD is used for replication, from if read (input file), to the of (output file).
If=/dev/zero does not produce IO, so it can be used to test the write speed, and the same of=/dev/null does not produce IO, which can be used to test the read speed.
BS is the size of each read or write, that is, the size of a block;
Count is the number of read-write chunks, multiplied by the amount of read and write data, the larger the amount of data (count), the more accurate, and the average of multiple tests.

Have you seen the difference between the three commands?

if=/dev/**, yes, the key is the parameters of the root behind dev/, do not use zero, parameters are explained, so that is not generated I/O. The measured data is inaccurate. So the results vary so much.

Note: Be sure to root the real device number (Input command df-th, can get, red part)

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All right, here it is!!

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About Linux under DD Test disk PIT!!