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I have to bought a SD card for my raspberry pi. It is better to have a huge writing speed (like 95 MB/s) or it is not so important and I can buy slower SD (30 MB/s or 45 MB/s) ?

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    As per my answer, you will never get speeds significantly above 20 MB/s on the SD card bus. However, that doesn't mean that faster cards aren't still faster: elinux.org/RPi_SD_cards#SD_card_performance So economics aside, yes a class 10 should be better. – goldilocks Dec 9 '13 at 15:34
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I have to bought a SD card for my raspberry pi. It is better to have a huge writing speed (like 95 MB/s) or it is not so important and I can buy slower SD (30 MB/s or 45 MB/s) ?

No matter what, you will not much exceed 20 MB/s (read or write) on the pi's SD card bus. Have a look at the chart here, and notice the very fastest write speeds are 21 or 22 MB/s. I've done my own test of class 4 vs. class 10 -- notice they had identical read speeds of ~20 MB/s indicating both cards were limited by the pi's SD card bus.

Subsequent to that, I got a Sandisk class 10, and it far out performs the (disappointing) write speed of the Adata class 10. Moral: don't buy a cheap class 10 card just to have a class 10 card.

This doesn't mean a class 4 is just as good as a class 10, either -- but you can read that chart yourself.

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It is not necessary to have the fastest writing speed.

A class 10 would only be advantageous if you wish to write a lot of video from the camera.

For most use a class 4 or 6 is perfectly adequate. You won't notice the difference when using the RPi for most normal applications.

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I would go with a cheap SD card and make a USB (3.0) setup. It's faster and you can overclock the system. and a 16 GB USB 3.0 is also cheaper than a class 10 SD.

The rasp only has USB 2.0 ports, but USB 3.0 sticks are faster internally, so they will be overall faster also on a 2.0 USB port.

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    Do you have any evidence that USB 3.0 will be noticeably faster? and not limited by the bus? – Steve Robillard Dec 9 '13 at 16:43
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I have two Kingston 16GB memory cards, a class 4 & a class 10, otherwise identical.

I tested both, measuring boot time, using exactly the same version of Rasperian (Nov 2016) on identical Raspberry Pi's side by side.

The class 10 boots up in: 22 seconds.
The class 4 boots up in: 80 seconds.

So class 10 massively out performs the class 4, in my testing.

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It depends on your application. If you need a lot of space for your application, get a class 4 SD. They're cheaper. However, if you're doing something like a media center where read speeds are important and you're using an external drive for storage, get a small(2GB or 4GB) class 10.

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One thing to consider is also the write and especially read-speed on small files!

Sadly class 10, 4, etc. or even the maximum write speeds like 45 MB/s or 90 MB/s are no indication whatsoever for that. It really makes a difference in performance though (in general operating system speed for example).

Unless you are just handling "big" files, like it being a FTP-Server with only video files (which also most likely would have the network speed as bottleneck), not using the card that much at all, or when you have a lot of CPU heavy tasks and the processor is the main bottleneck instead.

Edit: Here is a nice list of benchmarked cards

  • So which SD card do you use then ? :) THis does make sense but using class 10, even on smaller files is better than 4. Also there is somekind of new firmware being rolled out to all these nand chips to speed up write times for many small files and improve ware out. LOL, I use Kingston Class 10 which are bottom and mid, but there is nothing to tell what the differecne is. Whaaa? – Piotr Kula Jul 16 '14 at 14:29
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    @ppumkin: To be honest, I am simply going with one of those class 10, 90MB/s (or similar) that shows reasonable bench performance on small files, while being still affordable. I am sure you could find something better (+ possibly at the same time cheaper) for the pi if you look hard enough. But for the time it takes to sift through every bench on the net, while increasingly being endangered of becoming insane, it is not worth it for me. From bench resuls and price I would recommend the Kingston Class10 32GB, but it has stopped working for a bunch of people, after some time.. (amazon reviews) – Levite Jul 16 '14 at 15:19

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