lvm resizing and shifting

[Craig White]

On Sat, 2008-08-23 at 20:09 +0200, Roberto Ragusa wrote:
> Craig White wrote:
> > I was able to reduce the size of the logical volumes, move the logical
> > volumes so they are adjacent and then reduce the size of the physical
> > LVM but I cannot seem to reduce the partition itself and I'm gathering
> > that this may not be possible.
> > 
> > # pvdisplay
> >   --- Physical volume ---
> >   PV Name               /dev/sda2
> >   VG Name               VolGroup00
> >   PV Size               95.00 GB / not usable 31.81 MB
> >   Allocatable           yes
> >   PE Size (KByte)       32768
> >   Total PE              3039
> >   Free PE               127
> >   Allocated PE          2912
> >   PV UUID               oAYcCQ-5n28-0C6i-1LLE-voCR-E19v-SQYQK0
> > 
> > # fdisk -l /dev/sda
> > 
> > Disk /dev/sda: 203.9 GB, 203928109056 bytes
> > 255 heads, 63 sectors/track, 24792 cylinders
> > Units = cylinders of 16065 * 512 = 8225280 bytes
> > Disk identifier: 0x00086350
> > 
> >    Device Boot      Start         End      Blocks   Id  System
> > /dev/sda1   *           1          13      104391   83  Linux
> > /dev/sda2              14       24792   199037317+  8e  Linux LVM
> > 
> > # df -h
> > Filesystem            Size  Used Avail Use% Mounted on
> > /dev/root              88G   54G   30G  65% /
> > /dev/sda1              99M   36M   59M  39% /boot
> > 
> > so in the end, /dev/sda2 remains approximately 200G and even the
> > gpartd-liveCD cannot resize /dev/sda2   ;-(
> > 
> > Is it even possible?
> 
> What you are attempting is not a common way to use the LVM system.
> I often create many pv on one disk (sda2, sda3, sda4) just to avoid
> this kind of problems.
> 
> The pv is now 95G, so only the first 95G of sda2 are used (usable).
> Now, thinking about it, resizing sda2 could simply mean you
> have to delete and immediately recreate sda2 with a smaller size.
> We just have to be sure about where the pv metadata are stored.
> According to
> 
>    http://www.guug.de/lokal/rhein-main/2004-09-23/LVM2_sage_23.09.pdf
> 
> we learn that
> 
>    LVM2 format is an ASCII text format which is at the beginning,
>   after a disk label, of every PV in 2 copies by default
>    in large configurations...
> 
> so it is at the beginning of the pv.
> 
> The procedure I'd try (assuming I had a backup of everything, as
> _this is obviously dangerous_):
> 
> 1) Boot from CD and without any kind of lvm detection.
> 2) Destroy sda2 and recreate it as 100G.
> 3) Boot the system again, check that the LVM is OK and
> pvresize sda2 in automatic size (so it goes from 95G to 100G).
> 
> Step 3) avoids that you have to calculate the new size for sda2,
> which is very difficult because of the partition and LVM roundings.
> 
> If you find the courage to try this, let me know how it went.
> 
> :-)
----
well the guinea pig wants to report - it worked ! ! !

# fdisk -l /dev/sda

Disk /dev/sda: 203.9 GB, 203928109056 bytes
255 heads, 63 sectors/track, 24792 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00086350

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14       12172    97667167+  83  Linux

I have free space...(I have to go back and now and pvresize to reclaim a
few gigs from the pv but the theory was terrific)

Thanks

Craig