5 microSD cards benchmarked
5 microSD cards benchmarked / Photo © Jean Georges Perrin

When you design a computer, whatever its usage is (server, desktop, IoT), at some point, you need to think about storage. This is no different with the Raspberry Pi. Sure, the specifications are pretty straight forward and what you need is a microSD card. A quick look on Amazon.com gives you roughly 270,135 results… And now?

In a project where I want to use my Raspberry Pi as a database server, I wanted to make sure that the storage will not be the bottleneck. When I started studying the storage part, I was not expected to find such differences in results. Some cards clearly did not behave the way they were supposed to.

Methodology

Prior to testing, I wanted to define metrics and a reproducible method. I have some microSD cards, more are coming to the market everyday, so, in order to make the test compatible with the future, I wanted to make sure that the method is documented and proofed.

I am running several sets of tests:

  • Writing of an image to the card.
  • Various reading tests.
  • Various writing tests.

The first test will only measure the bandwidth (or throughput, or data transfer rate) of the card during a “big” write operation. The measure will be in B/s (byte per second).

The reading and writing tests will measure both the throughput and the number of IOPS (Input/Output Operations Per Second).

For more information:

The details of the processes and tests will appear in a future article (update 2016-03-10, you can now read about the methodology of benchmarking.) Tests have been made using a Raspberry Pi 2.

Five microSD Cards

Brand SanDisk SanDisk SanDisk SanDisk Samsung
Model Ultra Ultra PLUS Ultra PLUS Extreme EVO
Capacity 64 GB 64 GB  64 GB  64 GB  64 GB
Visual differences Made in China, black PCB, back is flat, red background on front is darker Made in Taiwan, green PCB, back is slightly bumped, red background on front is lighter
Identifier 6403 6402 6401 6405 6404

The identifier is a unique number attached to the microSD cards, to make sure I test and handle the right one.

Results

Pure Writing Test

The pure writing test consists of writing about 4GB of data using the dd command on a MacBook Air, it does not involve the Raspberry Pi.

Brand SanDisk SanDisk SanDisk SanDisk Samsung
Model Ultra Ultra PLUS Ultra PLUS Extreme EVO
Identifier 6403 6402 6401 6405 6404
Writing speed (MB/s) 21.05 14.91 47.04 55.01 22.07

Raspberry Pi Reading Test

The reading tests are composed of 4 tests of 1, 2, 4, and 6 simultaneous processes reading 128MB on the Raspberry Pi 2, Model B. The first test measures IOPS, the second test measures throughput.

The greener it is, the higher the performance is. The orange and red indicate low performance.

Brand SanDisk SanDisk SanDisk SanDisk Samsung
Model Ultra Ultra PLUS Ultra PLUS Extreme EVO
Identifier 6403 6402 6401 6405 6404
IOPS
Test with 1 reader 1119 1240 1854 1803 1986
Test with 2 readers 1421 1300 2283 2158 2382
Test with 4 readers 1424 1266 2280 2146 2012
Test with 6 readers 1434 1272 2214 2177 1890
 IOPS Summary
Average 1350 1270 2158 2071 2068
Weighted average 1405 1272 2217 2136 2011
Max 1434 1300 2283 2177 2382
Throughput (KB/s)
Test with 1 reader 4476.1 4963.1 7419.5 7213.3 7946.7
Test with 2 readers 5687.3 5201.0 9137.0 8637.8 9533.2
Test with 4 readers 5708.7 5071.4 9130.5 8596.8 8058.6
Test with 6 readers 5750.2 5099.9 8872.5 8717.8 7573.5
Throughput (KB/s) Summary
Average 5405.6 5083.9 8639.9 8291.4 8278.0
Weighted average 5629.8 5096.2 8880.8 8552.5 8053.0
Max 5750.2 5201.0 9137.0 8717.8 9533.2

Raspberry Pi Writing Test

The writing tests are composed of 3 tests of 1, 2, and 4 simultaneous processes writing 2048MB (2GB) on the Raspberry Pi 2, Model B. As with the reading test, the first test measures IOPS, the second test measures throughput. I did not test the two first cards as reading performance was already bad.

Brand SanDisk SanDisk SanDisk SanDisk Samsung
Model Ultra Ultra PLUS Ultra PLUS Extreme EVO
Identifier 6403 6402 6401 6405 6404
IOPS     
Test with 1 writer 566 342 484
Test with 2 writers 417 351 370
Test with 4 writers 342 259 319
IOPS Summary
Average 442 317 391
Weighted average 395 297 357
Max 566 351 484
Throughput (KB/s)
Test with 1 writer 2264.8 1370.9 1937.2
Test with 2 writers 1672.2 1410.2 1482.7
Test with 4 writers 1376.4 1048.3 1284.6
 Throughput (KB/s) Summary
Average 1771.1 1276.5 1568.2
Weighted average 1587.8 1197.8 1434.4
Max 2264.8 1410.2 1937.2

Read / Write Ratio

The ratio between read and write indicates the card’s flexibility. If the card is going to be used in a camera, writing happens once per file then reading can happen one or many times. The scenario is different in a phone. I want to use those cards in database servers where there is constant I/O.

Brand SanDisk SanDisk SanDisk SanDisk Samsung
Model Ultra Ultra PLUS Ultra PLUS Extreme EVO
Identifier 6403 6402 6401 6405 6404
Ratio
IOPS 489% 653% 529%
Throughput 488% 650% 528%
Ratio on weighted average
IOPS 561% 719% 563%
Throughput 559% 714% 561%

Conclusion

All cards are definitely not equal.

The Samsung EVO’s performances decrease as you increase the load through the number or simultaneous processes.

The microSD card that is the most flexible and fits my needs is definitely the SanDisk Ultra PLUS. The performance are consistent through the load. However, I had 2 from different batches and I am a little worried about consistency. I will have to investigate more.

 

Updates:

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