I/O performance test for disk RAID5 and 10 using the DD tool

In many cases everyone is convinced of the theory, the theory is conditional, not all cases are correct. The company has a server, so the disk performance test, of course, the results of testing is only sequential I/O performance test (DD mechanism determined).

Prerequisites: (DELL R630 physical Machine test, memory 64G)
RAID5 5 block (600G SAS) + 1 (GHS)
RAID10 6 block (600G SAS) + 0 (GHS)
* When testing to ensure the authenticity of the test results, make sure that the test file size is much larger than the memory capacity.

First, disk write performance test
#dd If=/dev/zero of=/yc/itest.iso bs=1g count=1000 Conv=fdatasync

#dd If=/dev/zero of=/yc/itest.iso bs=1g count=1000 Conv=fdatasync

Second, disk read performance test
#dd if=/yc/itest.iso Of=/dev/zero bs=1g count=1000 iflag=direct

Appendix:
In general, we use the DD command to create a large file to test the read and write speed of the disk. However, many people have a misunderstanding that the DD command display speed is the disk write speed, in fact, this is otherwise. Let's examine how the DD command works.
1. DD If=/dev/zero of=/xiaohan/test.iso bs=1024m count=1
In this case, the speed at which the test is displayed is the speed at which the DD command writes the data to the memory buffer, and only when the data is written to the memory buffer that it starts to flash the data to the hard disk, so this time the data is not able to measure the disk write speed correctly.

2. DD If=/dev/zero of=/xiaohan/test.iso bs=1024m Count=1;sync
In this case, the test shows that the same situation is the same, two commands are executed successively, when sync starts to execute, the DD command has already printed the speed information on the screen, still cannot display the real speed from the memory to write the hard disk.

3. DD If=/dev/zero of=/xiaohan/test.iso bs=1024m count=1 Conv=fdatasync
When this parameter is added, the DD command executes to the end of a true "sync" operation, so you get the time it takes to read the 128M data into memory and write to the disk, so the time that is calculated is more realistic.

4. DD If=/dev/zero of=/xiaohan/test.iso bs=1024m count=1 Oflag=dsync
In this case, DD performs a synchronous write operation each time it executes. That is, this command to read 1M each time after the 1M is written to disk, and then read the following 1M, altogether repeated 128 times. This is probably the slowest way, and basically no write cache is used.

I/O performance test for disk RAID5 and 10 using the DD tool