I like to keep postgresql data and mail on completely separate independent partitions. If you are installing Debian from scratch and you use LVM with separate partitions for /home /var and /tmp (RECOMMENDED) then you can use the lvm tools to resize your /home partition to create space for /mailstore and /pgsql. If it is a server that is being installed at a customer’s site then I would also recommend creating a small partition to back up the conf files that you can mount manually but is not in fstab.

Shrinking the /home partition:  First you need to find out where it is by running

#lvdisplay

which should return information about each partition similar to

--- Logical volume ---
LV Path               /dev/caa-vg/home
LV Name              home
VG Name               caa-vg
LV UUID               xxxx-xxxx-xxxxxxx-xxxxxx-xxxxxx
LV Write Access       read/write
LV Creation host, time caa, 2016-05-04 22:17:43 +0100
LV Status             available
# open                1
LV Size               381.46 GiB
Current LE             97654
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           254:6

If you do not have Logical Volume Manager installed then do so:

#apt-get update && apt-get install lvm2

To reduce the partition simply run:

#umount /home
#lvreduce --resizefs -L 100G /dev/caa-vg/home
#mount /home

This will then change the partition size to 100GB so that you will have enough space to create the new partitions

Note caa-vg is the name of the volume group on our example machine.

To increase volume size of a partition run:

#umount /home
#lvextend --resizefs -L 100G /dev/caa-vg/home
#mount /home

To display the current size of the patition run:

#lvdisplay /dev/caa-vg/home

To create a new logical volume for the pgsql partition run

# lvcreate -L 100G -n pgsql caa-vg

This will create a 50GB logical volume called pgsql. Next you need to format the partition. The logical volume should have been created with the name /dev/caa-vg/pgsql you can check this by running lvdisplay

Now you need to create the filesystem:

#mkfs.ext4 -L pgsql /dev/caa-vg/pgslq

Now all you need to do is create a mount point and add it to /etc/fstab if you want it to mount automatically. If you want to mount it manually then run:

#mount /dev/caa-vg/pgsql /pgsql

from the command line

To list the partitions run

#lsblk

To display free space on the physical volume run

#pvs

or for the volume group

#vgs

Other useful commands that may be useful for recovering lost volumes.

• lvscan – displays information about logical volumens
• lvchange -ay /dev/volume-group/volume – sets an inactive volume to active
• vgscan – displays volume group names
• vgcreate – create a new volume group
• pvdislplay – shows information about physical volumes
• lvdisplay – shows volume information
• df -Th – shows the type (ext3, ext4, etc..) of the logical volumes
• fsck /dev/volume-greoup/logical-volume – checks the volume (can only be used when volume is not mounted)

Creating a new volume group from a new disk.

To do this the first thing you need to do is get os to see the disk.  First use lsblk to list the devices and determine which one you are looking for.

lsblk

this will generate output that looks something like

NAME                 MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda                    8:0    0 223.6G  0 disk 
├─sda1                 8:1    0   243M  0 part /boot
├─sda2                 8:2    0     1K  0 part 
└─sda5                 8:5    0 223.3G  0 part 
  ├─balsa--vg-root   254:0    0  23.3G  0 lvm  /
  ├─balsa--vg-swap_1 254:1    0    40G  0 lvm  [SWAP]
  ├─balsa--vg-var    254:2    0   8.4G  0 lvm  /var
  ├─balsa--vg-tmp    254:3    0   1.5G  0 lvm  /tmp
  ├─balsa--vg-home   254:4    0  54.5G  0 lvm  /home
  └─balsa--vg-xpws   254:5    0    80G  0 lvm  
sdb                    8:16   0 931.5G  0 disk 
sr0                   11:0    1  1024M  0 rom

Select your disk and create a volume group with vgcreate.  If for some reason this fails try using pvcreate to make the logical volume manager aware of the disk

vgcreate caa-data-vg /dev/sde /dev/sdf

You can then go on to create you volume groups etc. as described at the top of this page.

NOTE:  In most cases it makes no sense to create multiple partitions on the same disk when using LVM as you use it to manage the volumes.

If you want to extend and existing volume group with a new disk then you can use vgextend

vgextend caa-daa-vg /dev/sdb

Where /dev/sdb is your new disk.

 

EFI Boot disks

There are times when you may want more than one partition on a disk with some as logical volumes and others as ordinary partitions.  If you are installing an operating system on a UEFI machine for example then you need to format a small partition for grub.  To do this use your favourite disk partitioning tool to create the partitions and then you can select one of those partitions for your logical volume and leave the other outside of it.

Assuming you have an EFI partition (/dev/sda1) and a second partition (/dev/sda2) on your drive then you can simply create a volume group using the second partition in the normal way using vgcreate.