[Discuss] noise

[Alan W. Irwin]

On 2006-05-06 15:49-0700 David Bronaugh wrote:

> Alan W. Irwin wrote:
>> On 2006-05-06 13:07-0700 David Bronaugh wrote:
>> 
>>> I'm going to be experimenting with something interesting in this 
>>> regard... CF->IDE adapters, and high speed compact flash cards. This 
>>> would eliminate the remaining noise in my laptop, as there would be no 
>>> moving parts at all.
>> 
>> Doesn't compact flash memory have a limit on the number of rewrites before
>> it dies?  I believe there is a filesystem that attempts to reduce rewrites
>> because of this issue.  Is that how you plan to reduce the impact of this
>> issue?
> JFFS2 does this. However, it only operates on NAND flash devices driven by 
> the mtd layer.
>
> Compact Flash cards -do- however implement wear levelling, spare sectors, and 
> ECC. The number of writes ranges between 10,000
> and 100,000; in practice, I don't think this'll be a problem.

Do USB keychain drives also have all these CF protections against wear from
writes?  If write wear is not too much of a problem for those devices, it
would be fun to put a full heavily used Linux distro on one of those.

That's an interesting point about wear leveling which I am sure helps a
tremendous amount, but of course anything you can do to reduce writes will
extend your overall CF disk life.

There are some parts of the system that tend to be written a lot such as
/tmp and /var/log.  (I didn't mention swap in that list since I am assuming
here you have plenty of RAM so that swap is essentially unused).  You could
put /tmp and /var/log on a RAM filesystem, but maybe that is too specific
about which part of your filesystem has the hotspot for writes.  I wonder if
the best method of reducing CF disk wear would be to tune your kernel to
make it extremely reluctant to write a file actually to disk.

Anyhow, just some food for thought about an interesting technical problem.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the Yorick front-end to PLplot (yplot.sf.net); the
Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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