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Re: A stern warning of things to come



> This is not without problems, though:
> 
> (1) It's possible some PXE implementations will not like downloading a single
> 100+ MB image.  I'm hoping the number of machines affected is decreasing every
> year and we can rapidly stop caring.

This is actually of some concern, primarily that downloading within PXE
(of any type) is quite slow.  It's doable, but there are a few PXE
stacks that will barf on something that big.  Some of those can be
"fixed" by chaining first to gPXE then to the install.

That said RIP, which I've got in BKO, has an initrd that's about 100M in
size, and it works.  Just takes forever to load.

Case in point:

http://boot.kernel.org/bko/pxeknife/linux_boot_disks/rip/tftpboot/rootfs.cgz

is an initrd of roughly the size your proposing, and one I know works.

Various download times:

the above link with wget across the internet to my home:

69s - 1.37 MB/s

With tftp from a server in my house to my laptop (with a wifi link involved)

6:15.60 - 262 KB/s

Same tftp server only only wired (100mbps)

43.034s - 2.1 MB/s

NOTE: this is using the tftp client thusly:

time echo "get rootfs.cgz
quit" | tftp <server>

tftp implementations in PXE stacks are quite a bit slower than this.

> (2) The kernel may freak out about storing such a large image in memory so
> early on.  Peter has some thoughts about this.

I haven't seen any problems with this specifically.

> (3) Memory requirements may be increased.

It would effectively kill off anything with less than 256M of ram from
doing an install.  I wouldn't think this is common anymore, but I know
machines with 512M of ram are still in production today, and running Fedora.

> (4) Doing a large number of PXE-based installs all at once could perhaps bring
> a network to its knees.  Transferring a large number of copies of a large file
> all at once is a sure sign of impending doom.

You won't hit this any more than you would normally.  The bottleneck is
going to be the tftp server in this case, it won't be the network.

> (5) We may rapidly be writing ourselves out of a job.

Doubtful ;-)

Just some thoughts, I'm not sure if this kind of change would ultimately
be good or bad.  The biggest problem I can see if the want for an ever
increasing initrd.

- John 'Warthog9' Hawley


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