Setting up Logical Volumes with LVM

2012-06-06T19:32:25Z

Silent:

[[Category:Storage]]
{{Tip|This process can be done automatically by using the [[setup-disk]] script, using the -L option.}}
This document how to create logical volumes in Alpine using lvm2.

LVM is collection of programs that allow larger physical disks to be reassembled into "logical" disks that can be shrunk or expanded as data needs change.

In this document we will use a [[Setting up a software raid1 array | software raid1 device]] as physical storage for our logical volumes. We will set up a swap partition and a data partition for [[Setting up a basic vserver | vservers ]]
=== Installing LVM software ===
First we need to load the kernel driver, ''dm-mod''

{{Cmd|modprobe dm-mod}}

We also want it to be loaded during next reboot.

{{Cmd|echo dm-mod >> /etc/modules}}

We also need the userspace programs.

{{Cmd|apk add lvm2}}

=== Preparing the physical volumes ===
First we need to tell LVM that the partition is available as a physical volume and can be added to a volume group. In this example we use a software raid array as physical volume.

{{Cmd|pvcreate /dev/md0}}

=== Preparing the Volume Group ===
We can then create a volume group and add the physical volume ''/dev/md0''

{{Cmd|vgcreate vg0 /dev/md0}}

If we later need more space we can add additional physcal volumes with ''vgextend''. All physcal disks/partitions added need to be prepared with ''pvcreate''.

=== Creating Logical volumes ===
In the volume group we can create logical volumes. To create a 1GB volume called ''swap'' and a 6GB volume called 'vservers'' on the volume group ''vg0'' we run

{{Cmd|lvcreate -n swap -L 1G vg0
lvcreate -n vservers -L 6G vg0}}

=== Display Logical Volumes ===
You can now se the logical volumes with the lvdisplay utility.

lvdisplay
--- Logical volume ---
LV Name /dev/vg0/swap
VG Name vg0
LV UUID a4NYOi-FQP6-Lj5Q-0TYk-Jjtk-Qxjt-nxeBPn
LV Write Access read/write
LV Status available
# open 0
LV Size 1.00 GB
Current LE 256
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:0

--- Logical volume ---
LV Name /dev/vg0/vservers
VG Name vg0
LV UUID 16VMmy-7I0s-eeoW-tL2V-JrlN-jM6C-d0wEg0
LV Write Access read/write
LV Status available
# open 0
LV Size 6.00 GB
Current LE 1536
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:1

=== Rename Logical Volumes ===

{{Cmd|lvrename /dev/vg0/vservers /dev/vg0/database}}

=== Extend Logical Volumes ===
If you want to add space and the volume has the room for it...

{{Cmd|lvextend -L +50G /dev/vg0/vservers}}

If you want to set the space to a new larger size...

{{Cmd|lvextend -L 10G /dev/vg0/vservers}}

=== Start LVM during Boot ===
We want lvm to init the logical volumes during boot. There is a boot service named ''lvm'' to do this. If your volumes are on raid, make sure that ''/etc/init.d/lvm'' is started after mdadm-raid.

{{Cmd|rc-update add lvm}}

Or, on Alpine Linux 1.8 or earlier:

{{Cmd|rc_add -s 12 -k lvm}}

=== Setting up swap ===
Now we have our devices in /dev/vg0 and can use them as normal disk paritions. To set up swap:

{{Cmd|mkswap /dev/vg0/swap}}

Add the following line to your ''/etc/fstab'':

/dev/vg0/swap none swap sw 0 0

=== Setting up /vservers partition ===
Finally we want to set up an XFS partition for /vservers.

Install xfsprogs.

{{Cmd|apk add xfsprogs}}

Create filesystem on /dev/vg0/vservers.

{{Cmd|mkfs.xfs /dev/vg0/vservers}}

Add the mount information to your /etc/fstab: NOTE:tagxid may cause this not to mount. Try this by hand and check dmesg to see if there are any errors

/dev/vg0/vservers /vservers xfs noatime,tagxid 0 0

Note that the ''tagxid'' option is specific for setting up vserver [http://oldwiki.linux-vserver.org/Disk+Limits disk limits] so it might be you don't want it. The ''noatime'' option is to increase performance but you will no longer know when files were accessed last time.

=== Starting localmount and swap ===

Now we can mount our partition.
{{Cmd|mount /vservers}}

Make sure we run ''localmount'' during boot too, and that it is done after lvm. In Alpine Linux 1.9 and newer this should not be needed

{{Cmd|rc-update add localmount boot}}

Or, on Alpine Linux 1.8 or earlier:

{{Cmd|rc_add -s 14 -k localmount}}

Start the swap service and make sure it starts during next reboot and that it starts '''after''' lvm.

{{Cmd|/etc/init.d/swap start
rc-update add swap}}

Or, on Alpine Linux 1.8 or earlier:
{{Cmd|/etc/init.d/swap start
rc_add -s 14 -k swap}}

=== More Info on LVM ===
These resources may be helpful:

* the [http://tldp.org/HOWTO/LVM-HOWTO/commontask.html common tasks] section in the [http://tldp.org/HOWTO/LVM-HOWTO/index.html LVM Howto]
* [https://wiki.archlinux.org/index.php/LVM Arch wiki page on LVM]
* [https://wiki.archlinux.org/index.php/Software_RAID_and_LVM Arch wiki page on RAID and LVM]

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Setting up Logical Volumes with LVM