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List Archive: gentoo-embedded
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To: gentoo-embedded@g.o
From: Peter Stuge <peter@...>
Subject: Re: quickpkg and PKG_INSTALL_MASK
Date: Thu, 26 Jan 2012 15:59:20 +0100
Joakim Tjernlund wrote:
> > > You still want to pick a r/w branch with a filesystem that
> > > handles power cuts well.  You can continue to use JFFS2.
> >
> > Thought: Is there any evidence that one modern filesystem is better
> > than another with regards to sudden power removal?  You probably
> > need to speak to filesystem experts at this point and define the
> > kind of thing you are trying to protect against?  Sounds like you
> > have raw flash storage here, so that constrains your choices
> > somewhat?

In fact, having "raw" flash storage is the *only* way to have *any*
chance of completely reliable handling of power outage.


> AFAIK, only FSes which are designed for flash(JFFS2, UBIFS, YAFFS etc. )
> are safe w.r.t power cuts.

It's not only about the filesystem, it is also critical that the
kernel is actually in charge of writing to flash. This means that
if you are not using an mtd based device, you can never have perfect
reliability, regardless of what your filesystem promises.


> We are not using NAND flash yet but our next product will.

NAND or NOR is not important - mtd block device is.


> I do have the impression that any block emulating device such as
> SSD are unreliable w.r.t power cuts. I would love to be proven
> wrong though :)

Supposedly, Intel SSDs never report write completed before flash has
actually been updated. Good luck verifying that.

Everyone else buffers writes. The Samsung 830 series has 256MB of
SDRAM, and their multicore ARM controller handles the magic
buffering. Samsung 830 is built entirely by Samsung from Samsung
parts. All manufacturers besides Intel and Samsung use a mishmash
of components and firmware in their SSD products, and all do magic
buffering.


//Peter


Replies:
Re: quickpkg and PKG_INSTALL_MASK
-- Ed W
References:
quickpkg and PKG_INSTALL_MASK
-- Joakim Tjernlund
Re: quickpkg and PKG_INSTALL_MASK
-- Kfir Lavi
Re: quickpkg and PKG_INSTALL_MASK
-- solar
Re: quickpkg and PKG_INSTALL_MASK
-- Joakim Tjernlund
Re: quickpkg and PKG_INSTALL_MASK
-- Ed W
Re: quickpkg and PKG_INSTALL_MASK
-- Joakim Tjernlund
Re: quickpkg and PKG_INSTALL_MASK
-- Todd Goodman
Re: quickpkg and PKG_INSTALL_MASK
-- Ed W
Re: quickpkg and PKG_INSTALL_MASK
-- Joakim Tjernlund
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Updated Jun 25, 2012

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