Storage benchmark (hard disk or SSD)
Ways in which you can invoke
dd to test the write speed:
The default behaviour of
dd is to not “sync” (i.e. not ask the OS to completely write the data to disk before
dd exiting). The above command will just commit your 128 MB of data into a RAM buffer (write cache) – this will be really fast and it will show you the hugely inflated benchmark result right away. However, the server in the background is still busy, continuing to write out data from the RAM cache to disk.
Absolutely identical to the previous case, as anyone who understands how
*nix shell works should surely know that adding a
; sync does not affect the operation of previous command in any way, because it is executed independently, after the first command completes. So your (inflated) MB/sec value is already printed on screen while that sync is only preparing to be executed.
dd to require a complete “sync” once, right before it exits. So it commits the whole 256 MB of data, then tells the operating system: “OK, now ensure this is completely on disk”, only then measures the total time it took to do all that and calculates the benchmark result. Recommended to use. If your server or VPS is really fast and the above test completes in a second or less, try increasing the
count= number to
1024 or so, to get a more accurate averaged result.
Here dd will ask for completely synchronous output to disk, i.e. ensure that its write requests don’t even return until the submitted data is on disk. In the above example, this will mean sync’ing once per megabyte, or 256 times in total. It will be the slowest mode, as the write cache is basically unused at all in this case.
Perhaps not many people use this, but
dd in conjunction with any stream-processing CPU-intensive program can also be used as a simple CPU benchmark! It may be not very accurate, but the huge advantage is that it doesn’t require installing any additional software whatsoever, and typically you can run this “out of the box” on any GNU/Linux system. The usage is as follows:
In this case I used the
md5sum program, which calculates the MD5 hash of data that is fed to it. In effect,
dd here fetches 1 GB of zeroes from the Linux kernel, feeds that to md5sum, and then prints how fast in MB/sec that was processed. So for example on a modern 3.6 GHz AMD Phenom II CPU:
And on a VPS with a 2.1 GHz Opteron:
Generally on any modern 2.0+ GHz CPU you should be looking at a result of 200 MB/sec or more in this test. If you see very low results, like 20-40-50-100 MB/sec, it’s a sure sign that whatever system you’re running this on is either overloaded CPU-wise, or is hard-limiting your CPU allowance to only some portion of a full CPU core.
Basicly this post just copy and paste from here.