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

From: John Tetreault (blkthorn30_at_nospam@verizon.net)
Date: 07/20/03 

Date: Sun, 20 Jul 2003 02:55:48 GMT

Hell... Send it back to the hardware engineers and tell them to design
something that actually works... And "gone through initial qual-testing"...
I'd say somebody in QC should be fired for signing off on something with
that major of a design flaw. (Truth is, that is what you have... a design
flaw, that now some bean counter expects you to fix with software) Its the
old gigo principal... you can't take a piece of hardware that is unreliable
and unstable by design and make it reliable and robust with software. It
simply doesn't work. What kind of idiot hardware engineer would design a
piece of hardware that only gives you 1 second or less write time in event
of a power failure, especially in a system that is guaranteed to have power
failures on a regular basis? Anyone with half a brain would have thought...
gee, maybe some sort of battery backup would be a good idea here for when we
lose power... obviously they knew of the problem or they wouldn't have given
you the 1 sec cap power... but that also means they obviously could have and
should have, done more. 

-- 
----------
Hey, check out my web site at http://jht.hypermart.net/ for some great deals
on long distance and local phone service (3.9 cents per minute, saves me a
bundle every month!), cell phones, FREE pagers, computers, internet access
(dial up or DSL), digital satellite TV, home security systems and more, all
at great prices.
"Dan Harkless" <usenet@harkless.org> wrote in message
news:4189894b.0307171952.79189fe5@posting.google.com...
> steve@nospam.Watt.COM (Steve Watt) wrote in message
news:<HI6w3H.9Hu@Watt.COM>:
> > >My company is currently developing a Linux-based embedded device for
> > >installation on airliners.  The OS is based on SuSE 8.2 Pro's Minimum
> > >System install.
> >
> > Yikes, a certification nightmare from the start...
>
> Heh...
>
> > >Our device may lose power at any time, but it's very important we
> > >don't corrupt our data or our filesystem metadata, so our filesystems
> > >(except our initrd-based root filesystem) are ext3, mounted
> > >'data=journal'.
> >
> > As has been said many times through the thread, this is probably not
> > a good way to do things, because of how the ext3 journal is laid
> > out.
>
> And as I've said a couple of times, unless the ext3 journal causes an
> order of magnitude more writes to be done, or unless SanDisk's
> wear-leveling algorithm is bogus, I don't see how it's significant for
> Flash lifetime that we'll be using ext3 rather than ext2.
>
> > You've said, later in the thread, that you have a power-off detector
> > and a cap to provide some amount of run time after power failure.
> >
> > I'd solve this with two separate CF devices:  One to boot & root from,
> > that gets mounted read-only.  The other one holds volatile data.  Create
> > a ramdisk the size of the volatile data CF, and use that exclusively
> > until you get the power-off signal.  Then dump the whole thing to
> > the volatile data CF, while holding off writes as you had described
> > elsewhere.  You might even unmount the ramdisk (if possible) before
> > dumping it to the flash so the image is clean.
> >
> > You need to be sure you have enough time on the backup cap for that
> > write to complete, which shouldn't be all that much longer than
> > the worst case for a whole boatload of dirty cache blocks.
>
> No, we may accumulate many megabytes of data during a given uptime.
> I'm sure we wouldn't always have time to dump that to Flash during the
> 200ms - 1 sec. we'll have between the low-voltage signal and capacitor
> power drainage.
>
> > Depending on how large your budget is (we *are* talking aircraft
> > system prices, here), you could also go to some kind of battery-backed
> > RAM for the read/write filesystem, as well.  It's not that much more
> > expensive than CF, and you get more flexibility.
>
> Even if we're talking on the order of 256 MB worth?
>
> Unfortunately it's a moot point, because the hardware has already been
> designed, initial units built, and has gone through initial
> qual-testing.  Hardware was a done deal before I joined the company --
> now I and the other software engineers need to determine how to make
> it work and be robust and reliable.
>
> --
> Dan Harkless
> usenet@harkless.org
> http://harkless.org/dan/

Relevant Pages

  • Re: Have ext3 on SanDisk CF but cant disable write-back caching as kernel instructs
    ... Send it back to the hardware engineers and tell them to design ... of a power failure, especially in a system that is guaranteed to have power ... The other one holds volatile data. ...
    (comp.os.linux.hardware)
  • Re: Have ext3 on SanDisk CF but cant disable write-back caching as kernel instructs
    ... Send it back to the hardware engineers and tell them to design ... of a power failure, especially in a system that is guaranteed to have power ... The other one holds volatile data. ...
    (alt.os.linux.suse)
  • Re: Smart Battery System Design (was: Re: Question about userspace-consumer)
    ... It is quite old design. ... The machine eats non-trivial power while active, charger is ... back from suspend reliably due to the risk of hardware damage. ...
    (Linux-Kernel)
  • Re: Security and EOL issues
    ... OS software resources are designed that reserved ram and disk space among other resources, to reflect what current hardware size is available. ... (There was a security patch a few years ago that could not be applied to NT4 as it required more resources then NT4 could provide. ... Installing air bags requires that the automobile manufacturer design, test, ... Computer Emergency Response Teams, and Digital Investigations. ...
    (Security-Basics)
  • Re: 1/4 vs 1/2 wavelength antenna
    ... essentially its power supply ... He say's that if a design is done for conjugate ... The bottom line is that if I design an amp via load line techniques using the ...
    (sci.electronics.design)