[Fedora-livecd-list] RFC- unionfs persistence?

[Douglas McClendon]

Douglas McClendon wrote:
> While I haven't by any means given up pursuit of my devicemapper 
> implementation of persistence, I wonder-
> 
> What do people think about using unionfs for persistence (and perhaps 
> Copy-On-Write in general) in Fedora LiveCDs?
> 
> I was somewhat surprised to discover a while back that ubuntu actually 
> used devicemapper for their COW long ago (early 2005).  But that they 
> abandoned that in favor of the 'flexibility' of unionfs.
> 
> I know that unionfs was ruled out as an option for Fedora, because it 
> was being kept out of the repos.  In fact, before pilgrim/livecd-creator 
> came into existence, I posted a proof of concept fedora unionfs-based 
> livecd infrastructure-
> 
> http://www.redhat.com/archives/fedora-livecd-list/2006-April/msg00197.html
> 
> But a lot has changed in the last 18 months.  It seems that unionfs is 
> in the -mm kernel tree, and between that, fuse-unionfs, and aufs, it 
> seems pretty likely that some flavor of unionfs will make it into fedora 
> in the foreseeable future.
> 
> Given that, and given the multitude of other projects I could be working 
> on, makes me wonder how much time I should spend working on devicemapper 
> persistence, if the vast majority of livecds out there are using 
> unionfs, and unionfs may become an option for fedora in the near future.
> 
> Comments?

Never being one to avoid conversing with myself...

It occurs to me that it wouldn't be difficult at all to implement an 
initramfs system, that supports *BOTH* devicemapper and unionfs for COW. 
  With nothing more than a bootarg of cowmethod=<type> to specify 
changing from whatever the default method is to the other.

In this fashion, you could actually keep the existing devicemapper 
fedora livecd infrastructure, including the nice speedy installer :), 
and also support persistence via unionfs on the same livecd.

I still of course think that ubuntu made the wrong decision, and that 
devicemapper is ultimately more 'flexible' and better than unionfs.  But 
I can't deny that unionfs works easily in a lot of ways (spec wrt livecd 
persistence), and has certainly enjoyed widespread usage.

-dmc