[linux-lvm] Rezising root ("/") partition

Hugo Kawamorita de Souza hugo at icaro.com.br
Fri Nov 21 15:45:02 UTC 2003

Keywords to this subject: Linux LVM , root ( / ) partition / directory / 
filesystem rezize , vgreduce problem , filesystem / superblock info size greater 
than VG size , fsck ,  etc.

Hello guys,

I just would like write down the expirience I had yesterday, actually it spent 
the whole night, trying to resize a main file server root partition.

Our server runs a RedHat Linux 9.
My main difficulty was to umount the / partition in order to resize its 
filesystem. So I used the shell from the installation CD. I did the whole steps 
using that CD shell: create a new partition PV (I did not rebooted after this! 
Maybe it was the great fault), extended the VG, exnteded the LV and resized the 
filesystem. Then, I mounted the / partiton, executed a "df" which showed the new 
size of the / filesystem. So I rebooted the system, without the CD. And the nthe 
terrifying error: "the superblock says that the / filesystem has NEW_BIG_SIZE 
blocks, but the it only has OLD_SMALL_SIZE physical blocks. The partition table 
or the superblock information is wrong. run fsck to correct the error...".
So I gave the root password and tried to see what's happened. After all I found 
out that the new PV was contained in the root VG, the root VG had the new big 
size, the filesystem also had the new size, but if I remembered it right, the 
root LV was with the old small size and also the "allocable(?, or something 
like)" size of the root VG was the old small one. I could not resize the root 
filesystem and the root LV again and I could not remove the new PV from the root 
VG either. I tried to do "pvmove", etc, I just could do anything, and every scan 
and display said the thaere was no inconsistency. I knew about vgcfgrestore, but 
I was not able to make it work correctly.

Any way, let me try to try explain my solution too. 2 threads that helped me to 
figured out:

Fixing a VG with an empty borked PV

Help! unable to mount lv's - can't see why!

Using the rescue from the installtion CD, I had the thought to rollback what I 
have done, but I just could not remove the dammed new PV from the root VG. After 
a long time (I started all this at 7:00h PM of 2003-11-20, it was already 2:00 AM 
of 2003-11-21 and just finished all this at 4:15 AM of 2003-11-21) and after I 
did a backup of all our changed data on thsi server, I could try to do some 
operations not being so afraid. The root VG had already 2 partition PVs and I was 
trying to add another one. At some time, I was able to go vgcfgrestore of the 
root VG from /etc/lvmconf to the first 2 PVs. This backup was done automatically 
at some time before where the new PV was not contained the root VG. After the 
restore the root VG information show that the new PV was not in the root VG and 
the pvscan was saying that the new PV was in the root VG but it was INACTIVE: 
that was a good news for me. At this time I decided to delete that PV partition 
with fdisk,  after thsi the root VG has gone in inconsistency, so I did the 
vgcfgrestore again to the first 2 PVs and the VG became consistent again, GREAT! 
After thsi I was able to do all the process again:

_ using the Rescue CD
_ create the new partition again using fdisk
_ pvcreate
_ vgextend
_ resize the LV and the filesystem with e2fsadm (without, ignoring fsck, which 
reports some inconsistencies due the superblock stuff...)

After this I did a vgcfgbackup and copied it to my real /etc/lvmconf. I also 
copied the file /etc/lvmtab.d/<ROOT_VG> to my rela /etc/lvmtab.d .

Here I leave a question: is this really necessary? It worked for me after this, 
but I do not know if the LVM information goes to the correct place, so that after 
booting without the Rescue CD it will be effective.

So, my last night and my sleeping hours were spent with this...

I hope this could help someone else.


Hugo K.S.
LPI ID: LPI000032731

Hugo K. de Souza                Ícaro Technologies
Software Consultant             http://www.icaro.com.br
mailto:hugo at icaro.com.br        Av. Barão de Itapura, 950, 8o andar, Botafogo
Work: +55 19 3237-7878 Ext: 248 Campinas, SP, Brazil
Fax: +55 19 3237-7008           CEP: 13020-431

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