[linux-lvm] Shrinking LVM partition at beginning

[linux-lvm] Shrinking LVM partition at beginning

[Nick Urbanik]

Dear Folks,

I want to shrink an LVM partition and expand a preceding, non-LVM
partition.  The LVM partition contains three logical volumes.  I
shrank the larger, middle home volume at the volume's end successfully
with a command something like this:

sudo lvresize --verbose --resizefs -L -40G /dev/fedora/home

and then used pvmove to move all the pysical extents towards the end
of the disk, using some commands something like this:

sudo pvmove --alloc anywhere /dev/sda6:24387-34626 /dev/sda6:34627-44866

until all the extents are towards the end of the disk, and there are
10240 unused at the beginning of the volume.

So: can anyone suggest how I can shrink the volume group by that 10240
physical extents, so that I can shrink the partition, and expand the
previous partition?

Here are some details:
Fedora 23, i686, MBR partitioning.

[liveuser@samsung ~]$ sudo lvdisplay -m
  --- Logical volume ---
  LV Path                /dev/fedora/root
  LV Name                root
  VG Name                fedora
  LV UUID                C3JJJ0-L7dR-6kLJ-xj4U-zUn2-i9tY-bexbV1
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2013-10-20 18:39:46 -0400
  LV Status              available
  # open                 0
  LV Size                50.00 GiB
  Current LE             12800
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:3
   
  --- Segments ---
  Logical extents 0 to 12799:
    Type		linear
    Physical volume	/dev/sda6
    Physical extents	10240 to 23039
   
   
  --- Logical volume ---
  LV Path                /dev/fedora/home
  LV Name                home
  VG Name                fedora
  LV UUID                lHnoBw-pzJn-jCkZ-JaZ3-evAb-RisG-N22ErF
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2013-10-20 18:39:51 -0400
  LV Status              available
  # open                 0
  LV Size                85.26 GiB
  Current LE             21827
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:4
   
  --- Segments ---
  Logical extents 0 to 21826:
    Type		linear
    Physical volume	/dev/sda6
    Physical extents	23040 to 44866
   
   
  --- Logical volume ---
  LV Path                /dev/fedora/swap
  LV Name                swap
  VG Name                fedora
  LV UUID                HL6UPR-Z5AK-Oa6a-X9kZ-1wn0-j3Mn-w3avH9
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2013-10-20 18:39:56 -0400
  LV Status              available
  # open                 2
  LV Size                2.03 GiB
  Current LE             520
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:5
   
  --- Segments ---
  Logical extents 0 to 519:
    Type		linear
    Physical volume	/dev/sda6
    Physical extents	44867 to 45386
   
   
[liveuser@samsung ~]$ sudo vgdisplay 
  --- Volume group ---
  VG Name               fedora
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  28
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               1
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               177.29 GiB
  PE Size               4.00 MiB
  Total PE              45387
  Alloc PE / Size       35147 / 137.29 GiB
  Free  PE / Size       10240 / 40.00 GiB
  VG UUID               gAbhli-WPRu-ZOkx-nAbl-lPCD-An7E-uEmhO6
   
Any suggestions gratefully received.
-- 
Nick Urbanik             http://nicku.org           nicku@nicku.org
GPG: 7FFA CDC7 5A77 0558 DC7A 790A 16DF EC5B BB9D 2C24 ID: BB9D2C24

Re: [linux-lvm] Shrinking LVM partition at beginning

[Zdenek Kabelac]

Dne 9.4.2016 v 12:12 Nick Urbanik napsal(a):
> Dear Folks,
>
> I want to shrink an LVM partition and expand a preceding, non-LVM
> partition.  The LVM partition contains three logical volumes.  I
> shrank the larger, middle home volume at the volume's end successfully
> with a command something like this:
>
> sudo lvresize --verbose --resizefs -L -40G /dev/fedora/home
>
> and then used pvmove to move all the pysical extents towards the end
> of the disk, using some commands something like this:
>
> sudo pvmove --alloc anywhere /dev/sda6:24387-34626 /dev/sda6:34627-44866
>
> until all the extents are towards the end of the disk, and there are
> 10240 unused at the beginning of the volume.
>
> So: can anyone suggest how I can shrink the volume group by that 10240
> physical extents, so that I can shrink the partition, and expand the
> previous partition?

Hi

Unsupported - requires very good understanding about lvm2 metadata format
and very good precision in all calculations if you would do it by hand...

Basically you need to recreate PV header at different position,
and recompute all 'PV' extents in use.

IMHO easiest&safest for a normal user is to just 'copy' disk elsewhere, 
reformat with new layout and copy data back (yeah - takes some time,
but with significantly less probability of data loose...)

lvm2 is not meant to be used with other volume manager (like partitions)
so do not expect it will support such sort of operations...

Regards

Zdenek

Re: [linux-lvm] Shrinking LVM partition at beginning

[Alasdair G Kergon]

Outline of the process:

Work out the new layout as best you can.

vgcfgbackup the metadata into a text file.

Update partition table moving the start of the partition, being careful to
respect any alignment restrictions.

Edit the text file based on the new partition start location so that all the
data will be in the same place (so all extent numbers will be smaller by
the same fixed amount, and dev_size and pe_start values will change).

pvcreate with --restorefile and -Zn to format the "new" partition for LVM's
use based on the edited file.

vgcfgrestore from that file.

Alasdair

Re: [linux-lvm] Shrinking LVM partition at beginning

[Alasdair G Kergon]

On Sat, Apr 09, 2016 at 07:52:07PM +0200, Zdenek Kabelac wrote:
> Unsupported 

The process could easily be automated, but there just isn't enough
demand to justify spending the time writing and testing code for it.

An expert would also find it pretty easy to test each step as they
proceeded without making any irreversible changes that risked data
loss.  E.g. using device-mapper to try out the device in advance
of the partition table change with the PV header sectors mapped 
somewhere else and using some of the advanced lvm.conf options 
that take metadata from elsewhere.

Alasdair