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140 lines
6.0 KiB
Markdown
(translated by runningwater)
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Test read/write speed of usb and ssd drives with dd command on Linux
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### Drive speed ###
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The speed of a drive is measured in terms of how much data it can read or write in unit time. The dd command is a simple command line tool that can be used to read and write arbitrary blocks of data to a drive and measure the speed at which the data transfer took place.
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In this post we shall use the dd command to test and read and write speed of usb and ssd drives using the dd command.
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The data transfer speed does not depend solely on the drive, but also on the interface it is connected to. For example a usb 2.0 port has a maximum operational speed limit of 35 Mbytes/s, so even if you were to plug a high speed usb 3 pen drive into a usb 2 port, the speed would be capped to the lower limit.
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The same applies to SSD. SSD connect via SATA ports which have different versions. Sata 2.0 has a maximum theoretical speed limit of 3Gbits/s which is roughly 375 Mbytes/s. Whereas Sata 3.0 supports twice that speed.
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### Test Method ###
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Mount the drive and navigate into it from the terminal. Then use the dd command to first write a file using fixed sized blocks. Then read the same file out using the same block site.
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The general syntax of the dd command looks like this
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dd if=path/to/input_file of=/path/to/output_file bs=block_size count=number_of_blocks
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When writing to the drive, we simply read from /dev/zero which is a source of infinite useless bytes. And when read from the drive, we read the file written earlier and send it to /dev/null which is nowhere. In the whole process, dd keeps track of the speed with which the transfer takes place and reports it.
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### SSD ###
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The SSD that we are using is a "Samsung Evo 120GB" ssd. It is a beginner level ssd that comes within a decent budget and is also my first SSD. It is also one of the best performing ssds, in the market.
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In this test the ssd is connected to a sata 2.0 port.
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#### Write speed ####
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Lets first write to the ssd
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$ dd if=/dev/zero of=./largefile bs=1M count=1024
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1024+0 records in
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1024+0 records out
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1073741824 bytes (1.1 GB) copied, 4.82364 s, 223 MB/s
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Block size is actually quite large. You can try with smaller sizes like 64k or even 4k.
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#### Read speed ####
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Now read back the same file. However, first clear the memory cache to ensure that the file is actually read from drive.
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Run the following command to clear the memory cache
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$ sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"
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Now read the file
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$ dd if=./largefile of=/dev/null bs=4k
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165118+0 records in
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165118+0 records out
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676323328 bytes (676 MB) copied, 3.0114 s, 225 MB/s
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The Arch Linux wiki has a page full of information about the read/write speed of various SSDs from different vendors like Intel, Samsung, Sandisk etc. Check it out at the following url.
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[https://wiki.archlinux.org/index.php/SSD_Benchmarking][1]
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### USB ###
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In this test we shall measure the read and write speed of ordinary usb/pen drives. The drives are plugged to standard usb 2 ports. The first one is a sony 4gb usb drive and the second is a strontium 16gb drive.
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First plug the drive into the port and mount it, so that it is readable. Then navigate into the mount directory from the command line.
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#### Sony 4GB - Write ####
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In this test, the dd command is used to write 10,000 chunks of 8 Kbyte each to a single file on the drive.
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# dd if=/dev/zero of=./largefile bs=8k count=10000
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10000+0 records in
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10000+0 records out
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81920000 bytes (82 MB) copied, 11.0626 s, 7.4 MB/s
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So the write speed is around 7.5 MBytes/s. This is a low figure.
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#### Sony 4GB - Read ####
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The same file is read back to test the read speed. Run the following command to clear the memory cache
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$ sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"
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Now read the file using the dd command
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# dd if=./largefile of=/dev/null bs=8k
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8000+0 records in
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8000+0 records out
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65536000 bytes (66 MB) copied, 2.65218 s, 24.7 MB/s
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The read speed comes out around 25 Mbytes/s which is a more or less the standard for cheap usb drives.
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> USB 2.0 has a theoretical maximum signaling rate of 480 Mbits/s or 60 Mbytes/s. However due to various constraints the maximum throughput is restricted to around 280 Mbit/s or 35 Mbytes/s. Beyond this the actual speed achieved depends on the quality of the pen drives and other factors too.
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And the above usb drive was plugged inside a USB 2.0 port and it achieved a read speed of 24.7 Mbytes/s which is not very bad. But the write speed lags much behind
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Now lets do the same test with a Strontium 16gb drive. Strontium is another very cheapy brand, although usb drives are reliable.
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#### Strontium 16gb write speed ####
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# dd if=/dev/zero of=./largefile bs=64k count=1000
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1000+0 records in
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1000+0 records out
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65536000 bytes (66 MB) copied, 8.3834 s, 7.8 MB/s
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Strontium 16gb read speed
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# sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"
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# dd if=./largefile of=/dev/null bs=8k
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8000+0 records in
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8000+0 records out
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65536000 bytes (66 MB) copied, 2.90366 s, 22.6 MB/s
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The read speed is lower than the Sony drive.
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### Resources ###
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- [http://en.wikipedia.org/wiki/USB][2]
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- [https://wiki.archlinux.org/index.php/SSD_Benchmarking][1]
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----------
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About Silver Moon
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Php developer, blogger and Linux enthusiast. He can be reached at [m00n.silv3r@gmail.com][e]. Or find him on [Google+][g]
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--------------------------------------------------------------------------------
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via: http://www.binarytides.com/linux-test-drive-speed/
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译者：[runningwater](https://github.com/runningwater) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://wiki.archlinux.org/index.php/SSD_Benchmarking
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[2]:http://en.wikipedia.org/wiki/USB
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[e]:m00n.silv3r@gmail.com
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[g]:http://plus.google.com/117145272367995638274/posts |