On Mon, 1 Feb 2021 18:01:40 +0000, in gmane.comp.hardware.beagleboard.user
Chris Green <[email protected]> wrote:
>Does running of an SD card rather than the EMMC slow things down a
>lot? I have tried a bigger, newer SD card to see if it speeded
>things up but it doesn't seem to have had much effect.
>
Depending upon the SD card -- yes!
Note that "Class 10" cards are speed rated for STREAMING a single file
to/from a freshly formatted card (eg: video). "Class 2/4/6" cards are rated
for multiple small file writes&reads with fragmentation (eg: still photo
camera with some images deleted). Also note that all such are based upon
FAT file system -- not a journaling system.
Some card makers of "Class 10" cards take advantage of this, and fit
controllers on the card that can only track TWO "open" "allocation units"
-- the FAT table, and the data file. Every time the filesystem has to open
another file (and that happens a lot with journals -- write new contents
somewhere, write metadata to journal, sometime later wipe out original
metadata, followed by writing journal metadata and deleting journal) it has
to obtain a new allocation unit -- this involves closing and flushing the
current allocation unit to the memory, finding and erasing a free
allocation unit (erase is slow, as it has to set every bit in the unit to
"1" -- writing can only toggle a "1" bit to a "0"), then copying unchanged
data that might be in an old allocation unit before writing new data to
that unit.
Better cards will support 4 to 6 simultaneous open allocation units,
meaning one can be updating multiple files in parallel without forcing
erase cycles and copying partial units around.
From a post I made last March
>From a post (of mine) on the R-Pi group... Running the "Raspberry Pi
>Dramble microSD benchmarks".
>curl
>https://raw.githubusercontent.com/geerlingguy/raspberry-pi-dramble/master/setup/benchmarks/microsd-benchmarks.sh
>>benchmark.sh
>
>"bdr-" is the "buffered disk read" from hdparm
>"dd-" are, well, "dd"
>The rest are "iozone" results.
>
>The BBB has
> SanDisk Edge 8GB Class 4 HC I8227DTJLT009
>Not sure of the eMMC version
>The R-Pi3B+ has
> Kingston 16GB Class 10 HC I U1 SDC10G2/16GB N0581-002.A00LF
>
>
>metric BBB (SD) RPi3B+ eMMC
>bdr-MB 21.74 21.97 hdparm did not run (tried to access SD)*
>dd-sec 89.4367 67.4917 63.8932
>dd-MB 4.7 6.2 6.6
>write 1652 250 1814
>rewrite 2306 237 1888
>read 6371 5814 5039
>reread 6375 5798 5038
>ranread 5364 5138 3562
>ranwrite 1157 234 395
>
> The Class 4 SanDisk, in the 1GHz single-core BBB readily beat the Class
>10 Kingston in a 1.4GHz quad-core R-Pi3B+ in any meaningful test (the
>Kingston only won out on the "bdr" and "dd" test cases, and the BBB eMMC
>beat it on the "dd" test). {Note: I just reran on the SD card, and
>"write"/"rewrite" only showed 405/284, which still beats the Class 10 --
>suspect if I redid the test it might improve as the SD card may have
>remnants getting reused)
The SanDisk Class 4 was easily 8 times faster than the Kingston Class
10 for regular write, rewrite, and random write, and was also faster (if
not as much) for read/reread/random read.
--
Dennis L Bieber
--
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