Re: Very slow transfers to/from micro SD card on a RPi B+

2015-08-17 21:30 GMT+02:00 Michael van Elst <mlelstv%serpens.de@localhost>:

stephanwib%googlemail.com@localhost (Stephan) writes:

>I have just rebooted with WAPBL enabled. Some quick notes:

>-Sequential write speed is a little lower, around 5,4 MB/s.

WAPBL is rather slow on SD cards because SD cards are very slow
when writing small chunks. So even when WAPBL excels, like unpacking
lots of files or removing a directory tree, it is slow because the
sequential journal is written in small blocks.

That might be all right. However, creating many files becomes worse the more files are being created. That is on all kinds of devices I´ve seen.

This is from an amd64 server box with an aac raid controller.

/root/test/files> time seq 1 10000|xargs touch
    3.10s real     0.01s user     3.07s system
/root/test/files> rm *
/root/test/files> time seq 1 20000|xargs touch
    9.88s real     0.01s user     8.51s system
/root/test/files> rm *
/root/test/files> time seq 1 30000|xargs touch
   23.45s real     0.04s user    20.41s system
/root/test/files> time seq 1 40000|xargs touch
   43.35s real     0.05s user    38.32s system

That is clearly not linear.

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Michael van Elst
Internet: mlelstv%serpens.de@localhost
"A potential Snark may lurk in every tree."