risk factor - ext4 and disk corruption

[John Watlington]

The classic trigger for corruption problems (especially w. SD cards)
is sudden power off events.   I believe we now have the ability
to tell the EC to auto-power on the laptop, so you can just plug it
into a lamp timer set to cycle on/off every ten minutes or so
and let it run...

When you say that the entire 11.2.0 development cycle
was done with ext4, was that released and abused extensively ?

Cheers,
wad

On Sep 7, 2011, at 11:06 AM, Martin Langhoff wrote:

> A quick heads up -- we've seen Jon Nettleton hit some disk corruption
> repeatedly on his development/test machine. Diagnosis of the prob led
> us to http://dev.laptop.org/ticket/11210 (erase-blocks doesn't work
> with Toshiba eMMC devices - which is what we have on SKU 198 -
> membrane kb units) but it is unclear whether that is the issue.
> 
> This is one of our current risks -- it is a concern because we need to
> know real soon whether this is a hw issue (related to the eMMC parts)
> or not. We have hit corruption issues with ext4 in the past (#9513)
> and fell back to ext3. It is not clear however that ext4 is suspect:
> the whole 11.2.0 dev cycle was done under ext4 and no disk corruption
> incidents were reported AFAIK.
> 
> From IRC discussion -- he seemed to hit it while:
> - developing, compiling,
> - using an ext SD card
> - running a patched kernel and xorg
> - presumably crashing a lot
> 
> We need to consider action around this
> 
> - try to force the error -- I'll set up a test rig for this, applying
> unclean shutdowns on a couple of SKU198 units
> - keep our eyes open for disk corruption reports, specially in builds
> including the new gfx code
> - potentially switch back to ext3 in OOB
> 
> It is very hard to prove a negative - tracking this at
> http://dev.laptop.org/ticket/11220
> 
> cheers,
> 
> 
> 
> m
> -- 
>  martin at laptop.org -- Software Architect - OLPC
>  - ask interesting questions
>  - don't get distracted with shiny stuff  - working code first
>  - http://wiki.laptop.org/go/User:Martinlanghoff
>