How to benchmark sd card read/write speeds

I just got some 8GB SD cards from Hong Kong sold as CLASS 6, so I thought it was a good idea to test their performances.

Insert the sd card into the reader and mount it. We assume the device will be /dev/sdb mounted as /media/8gb.

Firstly check the read speed through the hdparm command using the option -tPerform device read timings

$ sudo hdparm -t /dev/sdb
 Timing buffered disk reads:   58 MB in  3.08 seconds =  18.81 MB/sec

Then when test the write speed with dd writing approx 1GB of data to the disk. This large number is because the filesystem on the device will speed up the transfer by caching the data if a small transfer is carried out.

$ dd count=1024 bs=1M if=/dev/zero of=/media/8gb/testfile
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 79.4985 s, 13.5 MB/s

At the end the SD card performances are:

  • Read: 18 MB/sec
  • Write: 13 MB/sec

This values are aligned with a good CLASS 6 sd card. Luckily I wasn’t cheated.

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