[Discuss] noise

[David Bronaugh]

Alan W. Irwin wrote:
> 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.
I'm not sure about USB thumb drives. They may or may not; I think 
they're a lot dumber than CF cards, so I'm less certain about what they do.
> 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.
Absolutely.
> 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.
I've already put /tmp on tmpfs on a few machines. Seems to work out fine.

As to /var/log... that's not such a good idea, since you'd like it to be 
preserved over a reboot.

The main thing, really, is to not put swap on it. Might get away with 
it, but in general it sounds like a bad idea.

As to making it write less often, laptop-mode does that.
> Anyhow, just some food for thought about an interesting technical 
> problem.
Absolutely :)

David