Re: [linux-pm] Dangers of touching disk between suspend and resume

[Peter Jones <pjones@redhat.com>]

On Thu, Nov 30, 2006 at 03:00:43PM -0500, I wrote:
> On Tue, 2006-11-28 at 17:37 +0100, Stefan Seyfried wrote:
> 
> > So it is a good idea to tell the engineer to do "mkswap" on the swap
> > partition before putting the disk into the replacement hardware.
> 
> Ugh, no it's not.  You really want the UUID on the swap area to remain
> the same.

In response, on Thu, 2006-11-30 at 21:13 +0100, Stefan Seyfried wrote:
> Well, but the system won't care because it won't resume?
> Or am i missing something?

And On Thu, 2006-11-30 at 15:42 -0500, Daniel Drake wrote:
> Why?
> 
> [not questioning your reasoning, this is coming from someone who knows
> very little about swap structure and what the UUID is used for]

You want to get rid of the resume metadata from it, but you don't want
to create a new swap structure.  Normally it's not a problem, but in
some environments, such as with shared-storage like in a SAN[1], we need
to be able to identify that a swap device is really the one we mean to
be activating; the UUID is one of the best pieces of data we've got.  So
you don't want to start over with a new swap partition, you want to
clear the resume data only.

Granted, I think most distros, if not all, and all the standard tools
totally muck up swap on shared storage right now[0].  But that's no
reason to advocate such a bad habit.  For FC/RHEL making this work right
is at least on my TODO list for the relatively near future.

[0] "swapon -a" activates everything it finds, and that's what most
distros do during boot.  If you can see other machines' swap devices,
that's bad.

[1] If you hate that example, another with the same problem is when
you're running a virtual machine which has its own physical disk
partitions, i.e. vmware with /dev/sdb as its disk.

-- 
  Peter


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