linux-ext4 - AW: ext4 filesystem bad extent error review

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Date:	Fri, 3 Jan 2014 19:21:32 +0100
From:	"Juergens Dirk (CM-AI/ECO2)" <Dirk.Juergens@...bosch.com>
To:	Theodore Ts'o <tytso@....edu>, Eric Sandeen <sandeen@...hat.com>
CC:	"Huang Weller (CM/ESW12-CN)" <Weller.Huang@...bosch.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: AW: ext4 filesystem bad extent error review


On Thu, Jan 03, 2014 at 19:07, Theodore Ts'o [mailto:tytso@....edu]
wrote:
> 
> On Fri, Jan 03, 2014 at 11:54:12AM -0600, Eric Sandeen wrote:
> > >
> > > This call chain only happens if the block device is mounted.
> >
> > Sure, but I thought that's what they were doing.  Maybe I misread.
> >
> 
> I thought this was in relation to doing what they called a "barrier
> test", where you are writing to flash device and then drop power, and
> then see if the CACHE FLUSH request was actually honored.  (And
> whether or not the FTL got corrupted so badly that the device brick's
> itself, as does happen for some of the crappier cheap flash out
> there.)
> 
> But I'm not sure precisely how they implemented their test.  It's
> possible it was done with the file system mounted.  My suggestion was
> to make sure that the flash was proof against power drops by doing
> this using a raw block device, to remove the variable of the file
> system.
> 

Just as a quick reply for today:
If I remember right, Weller has done the barrier test w/o file system
mounted. Weller can give more details when he is back in office.
However, these tests were done some while ago with another type of
eMMC.  

> Given that they've since reported that they can repro the problem
> using soft resets, it doesn't sound like the problem is related to
> flash devices not handling powe drops correctly 

I think so as well, for the same reason and also because our tests with
journal_checksum show the same problem w/o any checksum error.

> --- although given
> that I'm still getting reports of people who have had their SD card
> get completely bricked after a power drop event, it's unfortunately
> not a solved problem by the flash manufacturers yet....  or rather,
> the few (many?) bad apples give all low-end flash a bad name.
>
>
       	     	     	    	  			 - Ted

Mit freundlichen Grüßen / Best regards

Dirk Juergens

Robert Bosch Car Multimedia GmbH
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