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Are the data buses for microSD and internal flash separate?

asked 2014-02-06 20:32:45 +0300

00prometheus gravatar image

Does anyone know if there are separate physical buses to the microSD and the internal flash? If so, there might for example be a performance advantage to RAIDing a partition on the microSD with the internal flash, for example to speed up Swap-space.

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Have not tried it, but a simple "dd" test should be able to tell. If you can get i higher combined rate dd:ing from both devices than from either one by itself it should mean that you can improve performance by using both simultaneously.

sunkan ( 2014-02-06 23:04:55 +0300 )edit

Its hard to tell by a dd, there are so many software-side things, locks, caches and buffers that could make a test like that go wrong (either faster or slower). What I am hoping for is a clear answer from someone that knows how the hardware is actually built. Then we would at least know what is theoretically possible.

00prometheus ( 2014-02-07 01:47:31 +0300 )edit

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answered 2014-02-07 19:22:04 +0300

Hount gravatar image

updated 2014-02-10 18:26:33 +0300

It seems that they're using separate data buses.

First test, both internal flash and SD-card.

dd if=/dev/zero of=/home/nemo/Documents/zero.iso bs=512k count=20 oflag=dsync & dd if=/dev/zero of=/run/user/100000/media/sdcard/zero.iso bs=512k count=20 oflag=dsync

10 round average = ~14,48 MB/s for the internal flash

and simultaneously run test

10 round average = ~3,72 MB/s for the SD-card

Second test, internal flash only.

dd if=/dev/zero of=/home/nemo/Documents/zero.iso bs=512k count=20 oflag=dsync

10 round average = ~12,28 MB/s for the internal flash

Third test, SD-card only.

dd if=/dev/zero of=/run/user/100000/media/sdcard/zero.iso bs=512k count=20 oflag=dsync

10 round average = ~3,68 MB/s for the SD-card

All tests were run in turns so that first I ran test one, two and three, then again 1-2-3 until I had ten test results for each test. I even verified that both dd's ran simultaneously on test one by running them with time(testsline) and time reported almost exactly the same time as the longer dd reported, so the faster dd was run simultaneously.

I apologize for the small test size but I believe this gives answer to the question.

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Asked: 2014-02-06 20:32:45 +0300

Seen: 294 times

Last updated: Feb 10 '14