How to reduce a logical volume in GNU/Linux using LVM

Description: previously, on this post, I explain how to extend a logical volume using LVM. Now, I’m going to explain how to reduce it without data loss (if you aren’t using all the available space, of course). In this example, I’m going to reduce a logical volume called logical_volume1 belonging to the volume group volume_group1 to 85 Gb of disk space. It’s mounted on /mnt/logical_volume1 .

Steps:

1. Umount the logical volume: umount /mnt/logical_volume1
2. Make a backup of the logical volume
3. Check the filesystem integrity: fsck -f -y -v /dev/volume_group1/logical_volume1
4. Resize the filesystem to something smaller than the final size (around 80GB in this case): resize2fs /dev/volume_group1/logical_volume1 80000M
5. Check the filesystem integrity again: fsck -f -y -v /dev/volume_group1/logical_volume1
6. Reduce the logical volume: lvreduce -L 85G /dev/volume_group1/logical_volume1
7. Resize the filesystem to fit the logical volume: resize2fs /dev/volume_group1/logical_volume1
8. Check the filesystem to know whether the reduction went fine: fsck -f -y -v /dev/volume_group1/logical_volume1
9. Mount the logical volume: mount /mnt/logical_volume1

NOTE: if you aren’t careful with the disk space you are using and the final disk space you are going to be using, this operation can cause data loss. I recommend to backup the logical volume before the reduction and to use around 5GB of “safe space” while reducing the filesystem in order to avoid data loss.

How to backup a logical volume (snapshots) using LVM

Description: a snapshot is a copy of the state of a logical volume at a particular point. It’s created almost immediately, so it’s very useful to backup large logical volumes. In this example, I’m going to create a snapshot of a logical volume called logical_volume1 beloging to the volume group volume_group1.

Steps:

1. Check the size of the logical volume (LV Size): lvdisplay /dev/volume_group1/logical_volume1
--- Logical volume ---
LV Name /dev/volume_group1/logical_volume1
VG Name volume_group1
LV UUID AxihqP-Yt8l-5scY-bXNG-Bn5D-K3ms-X7v1Ys
LV Write Access read/write
LV Status available
# open 1
LV Size 200,00 GB
Current LE 6400
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:5

   Usually, snapshots are smaller than the original logical volume, but I recommend to use at least the same space.

2. Create the snapshot: lvcreate -L200G -s -n backup_logical_volume1 /dev/volume_group1/logical_volume1

The -s param tells lvcreate to create a snapshot instead of a normal logical volume.

How to extend a logical volume in GNU/Linux using LVM

Description: if you have created a logical volume (maybe following my previous post) and you want to increase its size (if you have enough physical space, of course), LVM can do that easily. In this example, I’m going to extend a logical volume called /dev/volume_group1/logical_volume1 mounted on /mnt/logical_volume1 adding 50GB of disk space which are available in the volume group volume_group1.

Steps:

1. Unmount the logical volume if it’s mounted: umount /mnt/logical_volume1
2. Extend the logical volume with 50GB: lvextend -L +50G /dev/volume_group1/logical_volume1
3. Check the volume group: e2fsck -f /dev/volume_group1/logical_volume1
4. Resize the filesystem on the logical volume (ext3 in this case): resize2fs /dev/volume_group1/logical_volume1
5. Mount the logical volume again: mount /mnt/logical_volume1

Extending a logical volume it’s a safe operation which doesn’t involve much downtime. This is one of the many advantages of using LVM to manage disk storage.

How to configure a network bridge in Debian / Ubuntu

Description: Following yesterday’s post, today I’m going to explain how to do the same in a Debian / Ubuntu system.

Installation:

Install the packages needed: apt-get install bridge-utils

Configuration:

• Edit /etc/network/interfaces and replace your eth1 config with this:

  auto eth1
iface eth1 inet manual

  auto br0
iface br0 inet static
address 192.168.1.100
network 192.168.1.0
netmask 255.255.255.0
broadcast 192.168.1.255
gateway 192.168.1.1
bridge_ports eth1
bridge_stp off
bridge_fd 0
bridge_maxwait 0

• Restart your network interfaces: /etc/init.d/networking restart

How to configure a network bridge in Red Hat / Fedora

Description: a network bridge is a forwarding technique very useful when you have to deal with virtualization and you want to give your virtual machines direct access to your real network, without using NAT.

In this example, I’m going to use a bridge (br0) to access a wired network interface (eth1). I use eth1 for the bridge instead of eth0 because I prefer to use the first network interface to access the machine using SSH and fix any problems that could appear while configuring the bridge.

Installation:

Use yum to install the packages needed: yum install bridge-utils

Configuration:

• Edit /etc/sysconfig/network-scripts/ifcfg-eth1 and write this (changing the HWADDR for the MAC address of your network card):
  
DEVICE=eth1
HWADDR=00:11:22:33:44:55
ONBOOT=yes
BRIDGE=br0

• Edit /etc/sysconfig/network-scripts/ifcfg-br0 with this content (change the IP related fields to fit your needs):
  
DEVICE=br0
TYPE=Bridge
ONBOOT=yes
DELAY=0
BOOTPROTO=static
BROADCAST=192.168.1.255
IPADDR=192.168.1.100
NETMASK=255.255.255.0
NETWORK=192.168.1.0
GATEWAY=192.168.1.1

• Add these lines to /etc/sysctl.conf in order to disable packet filtering in the bridge:
  
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0


  This improves the bridge’s performance. I recommend to use packet filtering in the computers which connect through the bridge, but not in the bridge itself.

• Apply the syscttl changes: sysctl -p /etc/sysctl.conf
• Restart your network interfaces: service network restart