lvm resizing and shifting

[Craig White]

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.
> 
> :-)
----
OK - makes sense and thanks for the concept.

By the way...in studying information on parted, it appears that it is 
not capable of resizing an LVM partition...which explains why I couldn't 
get anything done beyond lvresize/pvresize.

I'm currently backing up everything - which I probably should have done 
before I ever started but clearly, the steps you outline go beyond a 
simple leap of faith. Unfortunately, I am using a USB disk so the backup 
is quite slow - c'est la vie

To back up, I booted from CD #1 in rescue mode and am using the 
following command...

cp -ar /mnt/sysimage/* /mnt/usb

Does anyone think that there is a problem with this type of logic for 
backup in terms of preserving linked files, etc?

Obviously I will have all my user files so a complete wipe and clean 
re-install will only suck time but no important data and I've done it 
this way in the past but I keep wondering if I should have tar'd 
everything to the USB disk instead

Thanks

Craig