Re: [Suspend-devel] s2disk and raid

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Tuesday, 3 April 2007 18:34, Stefan Seyfried wrote:
> On Tue, Apr 03, 2007 at 05:55:21PM +0200, Tim Dijkstra wrote:
> > Hi,
> > 
> > I've got a bugreport [0] from a user trying to use raid and uswsusp. He's
> > using initramfs-tools available in debian. I'll describe the problem
> > and my analysis, maybe you can comment on what you think. A warning: I only
> > have a casual understanding of raid, never looked at any code related to it.
> > 
> > This is a setup where root maybe on raid, but swap isn't. Swap on raid
> > will be very difficult to support, I think.
> 
> "it depends" :-)

Theoretically (and I mean it), we can do that.

> > Now comes a crucial point. The script that finds the raid array, finds
> > the array in an unclean state and starts syncing.
> 
> bad. Don't do that. Data will be lost.
> 
> > After this, resume finds an image in the swap partition and starts the
> > resume process. Part of this process is freezing everything but itself,
> > which fails on the process/thread that does the syncing.
> > 
> > IMO, the problem comes from the fact we started syncing, before we could
> > start resume. 
> 
> Yes.
>  
> > Now the problem could theoretically be solved by not starting the
> > assembly of the array once it is discovered, but modifying the 
> > initramfs to do the assembly after we have had the chance to resume.
> 
> Yes.
> 
> > The debian-maintainer of mdadm thinks that the suspend process should
> > have left the array in a clean state, but this is IMHO impossible. We
> > are freezing userspace. A mdamd process looking after the array will
> > probably get into trouble if we come back from suspend and we have
> > done something to the array in the mean time.
> 
> Yes.
>  
> > What do you think?
> 
> You are right, he is wrong.
> Do not touch anything before resume.

Definitely.  The same applies to the built-in swsusp, BTW.