[linux-lvm] root filesystem in lvm

[linux-lvm] root filesystem in lvm

[Tobias Reber]

On a test system I have put the root filesystem into lvm. Everything works
fine, however during shutdown I cannot vgchange -a n to the volumegroup,
where the root filesystem sits. Does that any harm?
Also did anybody out there look into lilo in order to make the kernel
bootable from an lvm volume? IMHO lvm looks very keen especially if you have
large disks, where you still have only 8 partitions. I prefer having my
filesystem spread out into several partitions for /, /usr and so forth.
Tobias

Re: [linux-lvm] root filesystem in lvm

[Heinz Mauelshagen]

> 
> On a test system I have put the root filesystem into lvm. Everything works
> fine, however during shutdown I cannot vgchange -a n to the volumegroup,
> where the root filesystem sits. Does that any harm?

No it doesn't because "vgchange -an" does not write anything back to the
physical volumes these days.
The only cause for documenting this is to go the "clean" way to stop subsystems
before halt/reboot.

BTW: would you mind sending your solution to the list?
     Tried an hour or so by myself but run into trouble doing
     the switch from the boot partion to real-root-dev in a LV 8*(

> Also did anybody out there look into lilo in order to make the kernel
> bootable from an lvm volume?

Not that i'm aware of.


> IMHO lvm looks very keen especially if you have
> large disks, where you still have only 8 partitions. I prefer having my
> filesystem spread out into several partitions for /, /usr and so forth.

Yep.


Heinz
--

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Systemmanagement C/S                             Deutsche Telekom AG
                                                 Entwicklungszentrum Darmstadt
Heinz Mauelshagen                                Otto-Roehm-Strasse 71c
Senior Systems Engineer                          Postfach 10 05 41
                                                 64205 Darmstadt
mge@ez-darmstadt.telekom.de                      Germany
                                                 +49 6151 886-425
                                                          FAX-386
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Re: [linux-lvm] root filesystem in lvm

[Michael Marxmeier]

Tobias Reber wrote:
> On a test system I have put the root filesystem into lvm. 

I assume you are using initrd?

> Everything works fine, however during shutdown I cannot 
> vgchange -a n to the volumegroup, where the root filesystem sits. 
> Does that any harm?

I don't think so. All vgchange -an is supposed to do is unregister 
the volume group with the kernel. Since you are going to boot anyway 
it does not make a difference.
I had a short look at the source and it seems to be a nop anyway.

> Also did anybody out there look into lilo in order to make the 
> kernel bootable from an lvm volume? IMHO lvm looks very keen 
> especially if you have large disks, where you still have only
> 8 partitions. I prefer having my filesystem spread out into 
> several partitions for /, /usr and so forth.

While this should not be too hard i'm not sure if this makes sense. 
Why not designate a small boot area on the disk (/boot) which holds
the kernel image and a minimal recovery system and use a initrd?

However it should be possible to use LILO. As far as i understand 
LILO uses partition relative block numbers to load the kernel image. 
We just need to make sure that they are relative to the dos style 
partition. If included statically in the kernel the lvm driver could 
execute the equivalent of a vgchange -ay and we should be able to 
mount the root file system.
However this will lead to some kernel bloat as some of the code which
currently resides un user space in lvmlib and vgchange must also be 
present in the kernel.
 
For now i would suggest to make a small boot area and use initrd 
to switch to lvm. This will also nicely avoid any stupid BIOS
limitations.


Michael

-- 
Michael Marxmeier           Marxmeier Software GmbH
E-Mail: mike@msede.com      Besenbruchstrasse 9
Voice : +49 202 2431440     42285 Wuppertal, Germany
Fax   : +49 202 2431420     http://www.msede.com/

Re: [linux-lvm] root filesystem in lvm

[Tobias Reber]

Michael Marxmeier wrote:
>I don't think so. All vgchange -an is supposed to do is unregister
>the volume group with the kernel. Since you are going to boot anyway
>it does not make a difference.
>I had a short look at the source and it seems to be a nop anyway.
>
When I looked into the source, I saw that it does an fsync on the underlying
partitions. So I am not so sure, if it really does no harm. To my knowledge
all block devices go through the buffer cache. Don't they?
>> Also did anybody out there look into lilo in order to make the
>> kernel bootable from an lvm volume? IMHO lvm looks very keen
>> especially if you have large disks, where you still have only
>> 8 partitions. I prefer having my filesystem spread out into
>> several partitions for /, /usr and so forth.
>
>While this should not be too hard i'm not sure if this makes sense.
>Why not designate a small boot area on the disk (/boot) which holds
>the kernel image and a minimal recovery system and use a initrd?
That's what I do at the moment. But I do not really like it because my /boot
filesystem now resides in a dos partition, where I boot from. I should like
to have a self-contained linux system
Cheers
Tobias