Gentoo Archives: gentoo-embedded

From: Peter Stuge <peter@×××××.se>
To: gentoo-embedded@l.g.o
Subject: Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK
Date: Thu, 26 Jan 2012 15:05:27
Message-Id: 20120126145920.20149.qmail@stuge.se
In Reply to: Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK by Joakim Tjernlund
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

Subject Author
Re: [gentoo-embedded] quickpkg and PKG_INSTALL_MASK Ed W <lists@××××××××××.com>