Re: Have ext3 on SanDisk CF but can't disable write-back caching as kernel instructs

From: Bernhard Roessmann (roessmann_at_gmx.net)
Date: 07/17/03 

Date: Thu, 17 Jul 2003 09:24:47 +0200

> Forgot to address this in my previous reply -- when you say "MANY",
> are you saying an ext3 filesystem on CF will get written to on the
> order of 2-3x as much as an ext2 filesystem would get written to? Or
> are you saying it'll get written to an order of magnitude more?

Depends how you write your data and which journalling method you use.
The worst case is "data=journal", which journals all data and metadata.
So everything is written at least twice. And if you write very small
amounts of data, EVERY write updates at least 2 or 3 sectors.
Another problem is that the ext3 journal stays on the same sectors, so
if CF wear leveling don't work well (and noboday seems to know HOW it
really works), this sectors will wear out much sooner.

> If not the latter, I don't think we care. Our preliminary ad-hoc
> calculations based on how we *hope* the SanDisk wear-leveling works

Nobody seems to know how the SanDisk wear leveling EXACTLY works
So I would suggest to make some real tests and see how long the CF will
survive. I think this is the only way to get good informations about
that. I will try this myself in the next weeks with a 32MB "consumer
grade CF" and a 32MB "industrial grade CF" from SanDisk, but with ext2.
I will post the results in comp.os.linux.embedded.

> (today I was told they'll supposedly be getting back to us within a
> week with details on that) showed the CF ought to last in the
> thousands of years.

Please tell us the details here, this would be very interresting to
nearly all people using CF cards to store "technical data".

Regards, 

-- 
Bernhard Roessmann
Don't Fear The Penguins!

Relevant Pages