[linux-lvm] Howto create a Compressed ROM File initrd with lvmcreate_initrd

[linux-lvm] Howto create a Compressed ROM File initrd with lvmcreate_initrd

[Jan H. van Gils]

	Hi,

Thanks for reading,

I am using Debian as a distro and it usses a cramfs initrd file when it
boots.
Here is the output from the original initrd file and the one created by
lvmcreate_initrd.

1. Orginal
initrd.img-2.4.20-686:      Linux Compressed ROM File System data,
little endian size 2920448 version #2 sorted_dirs CRC 0x2e79d9f7,
edition 0, 1565 blocks, 200 files

2. lvmcreate_initrd
initrd-lvm-2.4.20-686.gz:   gzip compressed data, from Unix, max
compression


Has some of you myth have seen in earlier posting my system wil not boot
When I use the initrd I have created with lvmcreate_initrd.

Here is the message:
Kernel panic: VFS: Unable to mount root fs on 3a:00

So I think the problem has to do with the fact that my kernel expects a
cramfs initrd
File and not a gzip compressed.

Any idea's in howto solve this ?

Greetz Jan

----
With regards Jan H. van Gils
Internet web-page http://www.Knoware.NL/users/janvg/
Internet e-mail address JanVG@Knoware.NL
RIPE Whois JHG5-RIPE, 6BONE Whois JHG1-6BONE

Re: [linux-lvm] Howto create a Compressed ROM File initrd with lvmcreate_initrd

[Patrick Caulfield]

On Sun, Jan 26, 2003 at 10:28:17PM +0100, Jan H. van Gils wrote:
> 
> 	Hi,
> 
> Thanks for reading,
> 
> I am using Debian as a distro and it usses a cramfs initrd file when it
> boots.
> Here is the output from the original initrd file and the one created by
> lvmcreate_initrd.
> 
> 1. Orginal
> initrd.img-2.4.20-686:      Linux Compressed ROM File System data,
> little endian size 2920448 version #2 sorted_dirs CRC 0x2e79d9f7,
> edition 0, 1565 blocks, 200 files
> 
> 2. lvmcreate_initrd
> initrd-lvm-2.4.20-686.gz:   gzip compressed data, from Unix, max
> compression
> 
> 
> Has some of you myth have seen in earlier posting my system wil not boot
> When I use the initrd I have created with lvmcreate_initrd.
> 
> Here is the message:
> Kernel panic: VFS: Unable to mount root fs on 3a:00
> 
> So I think the problem has to do with the fact that my kernel expects a
> cramfs initrd
> File and not a gzip compressed.

Yes, the Debian kernels don't have ext2 compiled in TTBOMK, only cramfs.
Unfortunately, LVM likes to write to the root filesystem during vgscan and so
you can't use a RO filesystem like cramfs - which is why lvmcreate_initrd
creates an ext2 filesystem. Someone (I forget who) did some work on getting LVM
to work with the Debian mkinitrd stuff but it was quite complicated and wasn't
integrated by the mkinitrd maintainer.

The simplest wasy to acheive this is to build your own kernel with ext2 built in
and use that for the initrd.

Root on LVM is complicated anyway so if youre not prepared to do this then you
really shouldn't be trying root on LVM either....
 

-- 

patrick

Re: [linux-lvm] Howto create a Compressed ROM File initrd with lvmcreate_initrd

[lvm]

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On Mon, Jan 27, 2003 at 08:26:55AM +0000, Patrick Caulfield wrote:
> 
> Yes, the Debian kernels don't have ext2 compiled in TTBOMK, only cramfs.

That is my (very limited) Debian experience as well.  In fact my
experience with trying to do md RAID and LVM (including / on
LVM) with Debian was enough to make me not want to go back there.
Mandrake work[s|ed] a lot better for me.  Just more polished.

Sure I could build a custom kernel and install some tools and modify
the initrd creator on Debian, but I don't want to.  I have better
things to do with my time than build basic system tools.  Why spend
that time, when a distro vendor does it for me?

Mandrake supports all this stuff (and even has LVM creation support
available during install!) right out of the box.  In their 9.1 release
they will support creating / on LVM as well (I finally got off my ass
and submitted my patch to their installer to do it :-).

> Unfortunately, LVM likes to write to the root filesystem during vgscan and so
> you can't use a RO filesystem like cramfs - which is why lvmcreate_initrd
> creates an ext2 filesystem.

Right.  But in the final analysis, it is silliness.  The data that it
writes is thrown away when the initrd is thrown away anyway.

> The simplest wasy to acheive this is to build your own kernel with ext2 built in
> and use that for the initrd.

Right.  But there should be a switch to vgscan/vgchange to not write
data to the filesystem.  Maybe LVM2 makes this all go away.  I dunno.
I have not looked at LVM2 yet.

> Root on LVM is complicated anyway so if youre not prepared to do this then you
> really shouldn't be trying root on LVM either....

It's not complicated at all on a distro with good support of it.  Of
course that's not an excuse to not learn how it all works.  You will
need that knowledge if it breaks on you.

b.

-- 
Brian J. Murrell

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