Talk:RPi SD cards - Revision history

Lekensteyn: /* Benchmarks are unreliable */ new section

2013-05-10T14:00:45Z

‎Benchmarks are unreliable: new section

Simon Small: Comment for Performance section

2013-01-03T23:39:05Z

Comment for Performance section

Simon Small: Comments on page creation

2013-01-02T00:24:29Z

Comments on page creation

New page

This is a consolidation of the SD card information in one place; the SD card is an essential part of the Raspberry Pi and a card cannot be used elsewhere unless it is reformatted. Hopefully, this will provide a greater focus on the SD card.

The working / non-working verification data has been rebuilt from the history records of pages [[RPi_VerifiedPeripherals#SD_cards]] and the previous [http://elinux.org/index.php?title=RaspberryPiBoardVerifiedPeripherals&action=history RaspberryPiBoardVerifiedPeripherals]. The verification table is based on an initial work from [[User:83a/SD_Cards]]. Those pages had become extraordinarily long. I believe that I have checked the accuracy of the table, but have removed links to vendors, as there are often several vendors for each card. [[User:Simon Small|SimonSmall]] ([[User talk:Simon Small|talk]]) 00:24, 2 January 2013 (UTC)

← Older revision		Revision as of 14:00, 10 May 2013
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	Added the data from [[RPi_Performance#SD_card]]. I have not reformatted the table. [[User:Simon Small\|SimonSmall]] ([[User talk:Simon Small\|talk]]) 23:39, 3 January 2013 (UTC)		Added the data from [[RPi_Performance#SD_card]]. I have not reformatted the table. [[User:Simon Small\|SimonSmall]] ([[User talk:Simon Small\|talk]]) 23:39, 3 January 2013 (UTC)
		+
		+	== Benchmarks are unreliable ==
		+
		+	The current read and write speeds are unreliable, the method for determining them are not accurate. The commands that have been used for most benchmarks is:
		+
		+	dd if=/dev/zero of=~/test.tmp bs=500K count=1024
		+	dd if=~/test.tmp of=/dev/null bs=500K count=1024
		+	There is a fundamental flaw in this, its results are always higher than the actual read/write speeds because the filesystem cache is involved. This makes write performance pretty unpredictable because buffers are not flushed. I [http://elinux.org/index.php?title=RPi_SD_cards&diff=249740&oldid=249356 tried to improve] these benchmarks by adding timing information and '''sync''', but these are still imperfect.
		+
		+	What about testing read performance using:
		+
		+	dd if=/dev/mmcblk0 of=/dev/null bs=4M count=128
		+	Write performance is still tricky as the file system must be unmounted first when performing direct I/O (to avoid filesystem corruption). The best we can do is relying on fsync:
		+
		+	dd if=/dev/zero of=~/test.tmp bs=4M count=128
		+	In my measurements on a brand-new SanDisk Ultra class 10 SDHC 8GB, block sizes of 1M and 4M performed similar (13.1 MB/s and 13.2 MB/s respectively), this possibly results from the intermediate file system layer. Note: numbers with a ''k'' and ''M'' suffix are base-2, therefore when ''1M'' equals ''1024K''.
		+
		+	Question: should we move all old data to a new page and ask editors to re-do experiments and include new experiments on this page?

← Older revision		Revision as of 23:39, 3 January 2013
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	The working / non-working verification data has been rebuilt from the history records of pages [[RPi_VerifiedPeripherals#SD_cards]] and the previous [http://elinux.org/index.php?title=RaspberryPiBoardVerifiedPeripherals&action=history RaspberryPiBoardVerifiedPeripherals]. The verification table is based on an initial work from [[User:83a/SD_Cards]]. Those pages had become extraordinarily long. I believe that I have checked the accuracy of the table, but have removed links to vendors, as there are often several vendors for each card. [[User:Simon Small\|SimonSmall]] ([[User talk:Simon Small\|talk]]) 00:24, 2 January 2013 (UTC)		The working / non-working verification data has been rebuilt from the history records of pages [[RPi_VerifiedPeripherals#SD_cards]] and the previous [http://elinux.org/index.php?title=RaspberryPiBoardVerifiedPeripherals&action=history RaspberryPiBoardVerifiedPeripherals]. The verification table is based on an initial work from [[User:83a/SD_Cards]]. Those pages had become extraordinarily long. I believe that I have checked the accuracy of the table, but have removed links to vendors, as there are often several vendors for each card. [[User:Simon Small\|SimonSmall]] ([[User talk:Simon Small\|talk]]) 00:24, 2 January 2013 (UTC)
		+
		+	Added the data from [[RPi_Performance#SD_card]]. I have not reformatted the table. [[User:Simon Small\|SimonSmall]] ([[User talk:Simon Small\|talk]]) 23:39, 3 January 2013 (UTC)