Expanding an LVM partition at the front

[Matthew Saltzman]

I deleted the partition immediately in front of an LVM physical volume.
I'd like to use the freed space as part of the LVM volume group.  I know
I could create a new partition in the same place, make it a physical
volume and add it to the group, but because the space is contiguous, I
wondered if it is possible just to move the front of the existing PV
partition to include the freed space.  

I tried changing the start of the partition using fdisk, but then the PV
is no longer recognized by LVM.  I suppose that means that there is
information about the PV stored in a particular location at the front of
the partition.  Putting the starting point back makes the PV
recognizable again.

So is there a utility that can move the front of a physical volume
partition?  (gparted and fdisk apparently can't).

TIA.

[Matthew Saltzman]

On Mon, 2011-02-21 at 21:00 +0100, Roberto Ragusa wrote: 
>  On 02/21/2011 08:17 PM, Matthew Saltzman wrote:
>  > So is there a utility that can move the front of a physical volume
>  > partition?  (gparted and fdisk apparently can't).
>  
>  [...] 
>  Another probably much safer solution would be:
>  
>  - get a spare disk (even USB external one)
>  - create new PV, add to VG, pvmove your PV to the new PV
>  - destroy and recreate your PV
>  - pvmove from USB PV to enlarged PV
>  - remove USB PV
>  
>  This is less error prone. It can happen while the filesystem is R/W mounted too.
>   
That sounds like a better idea.  (Probably slower though.)

Thanks.

-- 
                Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs

[Roberto Ragusa]

On 02/21/2011 09:17 PM, Richard Shaw wrote:

>  I'm not positive this would work and it certainly isn't
> elegant but...
>  
>  Could you just:
>  - Create a partition in the space preceding the current partition
>  - Add the partition to the existing vg
>  - Allocate those extents to the current lv
>  - Expand the file system to fill the now extended lv.
>  
>  I don't even like the idea, I'm just wondering if it would work. I
>  don't see why this would be any different that allocating extents from
>  several drives to make one lv / file system... 
It works perfectly. I'm doing it all the time.

The original poster said he was evaluating this option too.

-- 
   Roberto Ragusa    mail at robertoragusa.it

[Richard Shaw]

On Mon, Feb 21, 2011 at 2:00 PM, Roberto Ragusa <mail(a)robertoragusa.it&gt; wrote:
>  On 02/21/2011 08:17 PM, Matthew Saltzman wrote:
> > I deleted the partition immediately in front of an LVM physical volume.
> > I'd like to use the freed space as part of the LVM volume group.  I know
> > I could create a new partition in the same place, make it a physical
> > volume and add it to the group, but because the space is contiguous, I
> > wondered if it is possible just to move the front of the existing PV
> > partition to include the freed space.
> >
> > I tried changing the start of the partition using fdisk, but then the PV
> > is no longer recognized by LVM.  I suppose that means that there is
> > information about the PV stored in a particular location at the front of
> > the partition.  Putting the starting point back makes the PV
> > recognizable again.
> >
> > So is there a utility that can move the front of a physical volume
> > partition?  (gparted and fdisk apparently can't).
>
>  What you are attempting is quite dangerous.
>
>  I don't know if automated tools exist for this, but you should
>  do this:
>
>  let's suppose you have this layout
>
>  partition 5 cyl 1600-1999 empty space
>  partition 6 cyl 2000-2999 existing PV
>
>  - destroy partition 5 and 6 with fdisk (not joking!)
>  - copy data from 2000-2999 to 1600-2599 (dd on /dev/sda with appropriate
> bs,seek,skip,count)
>  - now create partition 5 on 1600-2599
>
>  At this point you should have your PV available again and you
>  have simplified your problem to "I want to enlarge a PV", which you can do
>  with fdisk (part5 from 1600 to 2999) and pvresize.
>
>  Another probably much safer solution would be:
>
>  - get a spare disk (even USB external one)
>  - create new PV, add to VG, pvmove your PV to the new PV
>  - destroy and recreate your PV
>  - pvmove from USB PV to enlarged PV
>  - remove USB PV
>
>  This is less error prone. It can happen while the filesystem is R/W mounted too. 
I'm not positive this would work and it certainly isn't elegant but...

Could you just:
- Create a partition in the space preceding the current partition
- Add the partition to the existing vg
- Allocate those extents to the current lv
- Expand the file system to fill the now extended lv.

I don't even like the idea, I'm just wondering if it would work. I
don't see why this would be any different that allocating extents from
several drives to make one lv / file system...

Richard

[Roberto Ragusa]

On 02/21/2011 08:17 PM, Matthew Saltzman wrote:
>  I deleted the partition immediately in front of an LVM physical
> volume.
>  I'd like to use the freed space as part of the LVM volume group.  I know
>  I could create a new partition in the same place, make it a physical
>  volume and add it to the group, but because the space is contiguous, I
>  wondered if it is possible just to move the front of the existing PV
>  partition to include the freed space.  
>  
>  I tried changing the start of the partition using fdisk, but then the PV
>  is no longer recognized by LVM.  I suppose that means that there is
>  information about the PV stored in a particular location at the front of
>  the partition.  Putting the starting point back makes the PV
>  recognizable again.
>  
>  So is there a utility that can move the front of a physical volume
>  partition?  (gparted and fdisk apparently can't). 
What you are attempting is quite dangerous.

I don't know if automated tools exist for this, but you should
do this:

let's suppose you have this layout

partition 5 cyl 1600-1999 empty space
partition 6 cyl 2000-2999 existing PV

- destroy partition 5 and 6 with fdisk (not joking!)
- copy data from 2000-2999 to 1600-2599 (dd on /dev/sda with appropriate
bs,seek,skip,count)
- now create partition 5 on 1600-2599

At this point you should have your PV available again and you
have simplified your problem to "I want to enlarge a PV", which you can do
with fdisk (part5 from 1600 to 2999) and pvresize.

Another probably much safer solution would be:

- get a spare disk (even USB external one)
- create new PV, add to VG, pvmove your PV to the new PV
- destroy and recreate your PV
- pvmove from USB PV to enlarged PV
- remove USB PV

This is less error prone. It can happen while the filesystem is R/W mounted too.

-- 
   Roberto Ragusa    mail at robertoragusa.it