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

[Chris Lalancette]

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.

> 
> I need something similar to boot read-only OS images over PXE boot for 
> LTSP.  Upstream LTSP5 uses nbd to serve a raw squashfs image as a 
> network block device, which means only a tiny bit needs to be in the 
> initrd and very little memory overhead.  Parts of the read-only image 
> are streamed over the network on demand.

The problem with this is the same problem that a NFS/iSCSI root have;
namely, that you have to setup another service alongside the PXE to get
the data over.  That increases the server-side setup complexity,
something we are hoping to keep to a minimum with oVirt.

That's not to say that the method probably isn't preferable, in general,
however.  And it's definitely something that we can look at doing in the
future.  I'll have to take a closer look at the LTSP stuff at some point.

Chris Lalancette