SD / Filesystem write lags -- test?

James Cameron quozl at
Wed Jun 23 17:39:14 EDT 2010

On Wed, Jun 23, 2010 at 05:08:40PM -0400, Martin Langhoff wrote:
> you've mentioned some interesting details to our writes-to-SD-are-slow
> issues. Do we have a good scripted test that is current to the problem
> (as we understand it today)?

My calculations were based on an invalid assumption so I'll have to

Here's some ideas though:

1.  start with an empty journal, cover the camera lens, use Record to
take lots of photographs (the O game key is faster than clicking the
UI), then Alt/Tab to the journal, then measure the time it takes for all
the photographs to arrive,

2.  in the Terminal activity create a script that writes 500Mb of data
to a file, then waits for the writes to finish:

cat << EOF > write-500mb
dd if=/dev/zero of=file bs=1024k count=500
chmod +x write-500mb
time write-500mb
rm -f file

3.  as a baseline, using OpenFirmware, reflash the same laptop using
fs-update, measuring the time taken (it is displayed after fs-update
finishes), and calculate a rate based on number of blocks shown.

James Cameron

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