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is this normal or brand new sd card is faulty somehow?

Writing:

  dd if=/dev/zero of=~/test.tmp bs=500K count=1024
  501+0 records in
  501+0 records out
  256512000 bytes (257 MB) copied, 78.3388 s, 3.3 MB/s

and reading:

  root@raspberrypi:/home/pi# hdparm -tT /dev/mmcblk0
  /dev/mmcblk0:
  Timing cached reads:   304 MB in  2.01 seconds = 151.46 MB/sec
  Timing buffered disk reads:  50 MB in  3.09 seconds =  16.18 MB/sec

SD Card: Kingston 8GB Class4
kernel: Linux raspberrypi 3.2.27+ #250 PREEMPT Thu Oct 18 19:03:02 BST 2012 armv6l GNU/Linux

Should I change for some another SD card? I saw some tests and with class4 I should have better write speeds.

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The speed does not sound unreasonable. Different models of SD cards have very different performance. Also writing small pieces of data is much slower than one sequential write. See this question –  Frepa Nov 7 '12 at 13:23
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2 Answers

The 30Mb/sec sandisk Ultra cards write at a top format speed of 25Mb/sec using the win32 disk imager. I have seen as low as 4Mb/sec on stock 4Gb cards from Element 14.

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Class 4 SD cards are comparatively quite slow. As Frepa noted writing multiple files will be slower than one big file (the file allocation table will need to be modified for each file and there will be multiple reads to look for empty blocks.)

As well dd (aka disk destroyer) seems to be quite slow - I use a 16GB Class 10 Polaroid card and it took hours to make a backup. Not sure of your use-case but I would recommend BerryBoot if you want to try a few images - it's a multiboot loader and lets you load new images without having to overwrite the whole card.

Running gparted to remove all partitions, reformat as FAT32, and copy over the ~70mb of BerryBoot files takes a few minutes. Then all you have to do is boot your Pi with the prepared card and it will set up a BerryBoot loader partition (which boots first and allows you to select your image of choice), and a linux partition where your images will be stored. Makes setting up, changing, and playing with new images much faster.

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