[Fedora-livecd-list] Live ISO within initrd for PXE Boot?

[Daniel P. Berrange]

On Sun, Feb 17, 2008 at 10:16:58PM -0500, Chris Lalancette wrote:
> Warren Togami wrote:
> > http://git.fedoraproject.org/git/?p=livecd;a=commit;h=e0f0269d3a8f8f310e7c5fdfb8af45892f419c13
> >> The way it works is to bundle the complete ISO image inside the initrd.
> >> The kernel and (bloated) initrd are downloaded using PXE in the normal
> >> way, and the init script finds and loopback-mounts the ISO image and
> >> booting continues as normal.
> > 
> > Wow.  I don't mean to offend, but this seems like an incredibly bad way 
> > of doing this.  Isn't this really slow in the boot up because you must 
> > wait for the entire ISO to download?  It also requires the client to 
> > have more than enough RAM to have the entire ISO in memory?  It sounds 
> > like the entire memory used by the ISO remains unavailable to the booted 
> > system.
> 
> Well, it depends on your definition of "bad".  For the purposes I
> originally wrote it for, the ISO is going to be fairly small (~70MB or
> less), and the target machines will have a lot of memory.  So for that
> situation, it works well enough, doesn't waste an appreciable amount of
> memory, and fits into existing tools fairly easily.

Yep, the overhead in this context is utterly irrelevant. We're talking about
scenario where the host will be running all its storage over iSCSI with Gig-E
so 70 MB is nothing at all. The host will also be running multiple guest
VMs with multi-GB of of RAM allocated to guests, to 70 MB in memory is again
nothing at all.  And 70 MB host image size is before we've even got serious
about stripping down to minimal size. The simplicity of pulling down the ISO
in the initial TFTP request easily wins here.

Dan.
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