HOW TO BOOT YOUR ROOT FS OFF OF LVM
---

The following is an email I recieved from Michael, interspersed with my
own comments. [Also, it may not be valid for more up-to-date versions of
LVM, it was written back in the pre-1.0 days. -DJE.]

Date: Fri, 20 Oct 2000 23:41:44 +0200
From: Michael Muehrenberg <Michael.Muehrenberg@t-online.de>
To: Dominic J. Eidson <sauron@the-infinite.org>

Am Freitag, 20. Oktober 2000 23:39 schrieben Sie:
> Have a short/quick howto on setting up booting off of an initrd to allow
> the root filesystem (and others) to be on LVM?

It goes something like this:

Can i have my root filesystem in a logical volume? 

Yes you can. There's basic support since LVM 0.7 to create an initial ram 
disk containing the necessary executables, device specials etc. to switch to 
a logical volume containing a root filesystem. See script 
lvmcreate_initrd(8). 

lvmcreate_initrd creates a new compressed initial ramdisk 
in /boot/initrd.gz. The initial ramdisk contains all nec­ 
essary binaries, shared libraries and a linuxrc file to 
switch to a logical volume based root filesystem. To 
build an initial ramdisk for a not running but generated 
kernel add the KernelVersion parameter (for eg. 2.3.25) on 
the command line. 

The necessary actions to change your system into a "root 
on logical volume" one are: 

Create a small (~20MB) partition which is bios reachable 
to hold the /boot filesystem (if you already have a small 
partition based root filesystem this can as well be used). 

If you like to standalone boot from this partition in case of an emergency, 
copy all necessary binaries and libraries 
to that filesystem as well and create a corresponding 
/etc/lilo.conf entry. In order to be able to edit 
lilo.conf in case you booted standalone, you should move 
/etc/lilo.conf to /boot/lilo.conf and create a symbolic 
link to it in /etc instead. This is not needed if you 
have a boot/root floppy which contains the LVM binaries 
and the library in addition. 
Create all logical volumes you need (for root, usr, opt 
etc.), create filesystems in them, mount them and transfer 
all files from the partition based filesystems into the 
logical volumes based ones. 
You have to setup your /etc/lilo.conf with a boot configuration like:

image = /boot/vmlinuz 
initrd = /boot/initrd.gz
root = /dev/YourVG/YourRootLV
label = rootonlv
append = "ramdisk_size=8192"

Replace YourVG and YourRootLV by your actual volume group 
and root logical volume names. In addition to that your 
/etc/fstab in your root logical volume has to contain: /dev/YourVG/YourRootLV 

/     ext2   defaults   0   1
/dev/YourBootPartition       /boot ext2   defaults   0   2
/dev/YourVG/YourUsrLV        /usr  ext2   defaults   0   3
/dev/YourVG/YourOptLV        /opt  ext2   defaults   0   4

etc. 
You can use other supported filesystem types as well 
(reiserfs for eg.) in case you generated support for those 
into your kernel. Run lilo, reboot and try... 
The partitions containing the former /usr, /opt etc. 
filesystems can now be used as physical volumes. pvcre­ 
ate(8) them and add them for eg. to YourVG. 
lvcmcreate_initrd return 0 for success. 1 is returned in 
all other cases.


The only things I had to do, was uncompress and mount the initrd.gz image,
and remove the "insmod lvm" line - I was using a SuSE 6.4 install, and lvm
support was compiled into the kernel already.

After this it worked just fine.

Feel free to email me with any questions/comments - email address is
above.