Introduction to LVM: Part Two
If you need a refresher on where we are at this point please see Part 1 of our Introduction to LVM guide.
Now we have three logical volumes, but no actual filesystems so they won’t do us much good when trying to store data on them. We’ll create an ext3 filesystem on backup, an ext4 filesystem on nfs and a xfs filesystem on media
[telesto] (~) >>> mkfs.ext3 /dev/data/backup
mke2fs 1.42 (29-Nov-2011)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
327680 inodes, 1310720 blocks
65536 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1342177280
40 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
[telesto] (~) >>> mkfs.ext4 /dev/data/nfs
mke2fs 1.42 (29-Nov-2011)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
327680 inodes, 1310720 blocks
65536 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1342177280
40 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
[telesto] (~) >>> mkfs.xfs /dev/data/media
meta-data=/dev/data/media isize=256 agcount=4, agsize=131072 blks
= sectsz=512 attr=2, projid32bit=0
data = bsize=4096 blocks=524288, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Now we are ready to mount our logical volumes, so let’s create the mount points and get them all mounted:
[telesto] (~) >>> mkdir -p /var/{media,backup,nfs}
[telesto] (~) >>> mount /dev/data/backup /var/backup
[telesto] (~) >>> mount /dev/data/nfs /var/nfs
[telesto] (~) >>> mount /dev/data/media /var/media
[telesto] (~) >>> mount |grep '/var'
/dev/mapper/data-backup on /var/backup type ext3 (rw)
/dev/mapper/data-nfs on /var/nfs type ext4 (rw)
/dev/mapper/data-media on /var/media type xfs (rw)
Now we have a functional LVM system and we can read and write to the newly mounted partitions. For the volumes to be mounted on boot of course we need to adjust our /etc/fstab file. First we’ll make a backup in case anything gets borked and we need to rescue the system from boot up issues:
[telesto] (~) >>> cp /etc/fstab{,.bak}
[telesto] (~) >>> ll /etc/fstab*
-rw-r--r-- 1 root root 767 Apr 1 08:38 /etc/fstab
-rw-r--r-- 1 root root 767 Apr 10 08:49 /etc/fstab.bak
Now that we have a good backup we need to add the new mounts to the file. Using your favorite editor add the following entries to the /etc/fstab file:
/dev/data/backup /var/backup ext3 rw,noatime 0 0
/dev/data/nfs /var/nfs ext4 rw,noatime 0 0
/dev/data/media /var/media xfs rw,noatime 0 0
To test that we have everything done correctly we will now reboot. Execute the command shutdown -r now to reboot the system.
Once the system is back online we can run df -h or mount to make sure that everything we added to the fstab file automatically mounted on boot up.
[telesto] (~) >>> df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/telesto--vg-root 18G 1.5G 15G 9% /
udev 989M 4.0K 989M 1% /dev
tmpfs 200M 276K 200M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 998M 0 998M 0% /run/shm
/dev/mapper/data-media 2.0G 33M 2.0G 2% /var/media
/dev/sda1 228M 54M 163M 25% /boot
/dev/mapper/data-backup 5.0G 139M 4.6G 3% /var/backup
/dev/mapper/data-nfs 4.8G 10M 4.6G 1% /var/nfs
As I mentioned previously one of the real benefits of LVM is the ability to resize Logical volumes and now we can take that a step further and resize not only the volumes but their respective filesystems as well. The first volume we are going to deal with is our logical volume backup.
First we need to umount the volume
[telesto] (~) >>> umount /var/backup
[telesto] (~) >>> mount|grep backup
If the umount was successful you should get no outout from the mount|grep backup command (provided you have no other mounts with the name backup in them).
Now let’s enlarge backup from 5GB to 10GB
[telesto] (~) >>> lvextend -L10GB /dev/data/backup
Extending logical volume backup to 10.00 GiB
Logical volume backup successfully resized
This of course only enlarges the logical volume and not the filesystem. To enlarge the filesystem we need to use the commands e2fsck and resize2fs
[telesto] (~) >>> e2fsck -f /dev/data/backup
e2fsck 1.42 (29-Nov-2011)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/data/backup: 11/327680 files (0.0% non-contiguous), 55935/1310720 blocks
We need to make a note here about the total block amount (1310720) for when we shrink the volume later in this guide.
[telesto] (~) >>> resize2fs /dev/data/backup
resize2fs 1.42 (29-Nov-2011)
Resizing the filesystem on /dev/data/backup to 2621440 (4k) blocks.
The filesystem on /dev/data/backup is now 2621440 blocks long.
Now that we have successfully enlarged the logical volume backup and resized the filesystem we will need to remount it:
[telesto] (~) >>> mount /dev/data/backup /var/backup
[telesto] (~) >>> df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/telesto--vg-root 18G 1.5G 15G 9% /
udev 989M 4.0K 989M 1% /dev
tmpfs 200M 276K 200M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 998M 0 998M 0% /run/shm
/dev/mapper/data-media 2.0G 33M 2.0G 2% /var/media
/dev/sda1 228M 54M 163M 25% /boot
/dev/mapper/data-nfs 4.8G 10M 4.6G 1% /var/nfs
/dev/mapper/data-backup 9.9G 140M 9.3G 2% /var/backup
If we need to shrink a logical volume we actually need to work in the reverse order. The first step is to shrink the filesystem and then we can actually reduve the logical volume itself. Let’s pick on the backup volume one more time. First step as always is to umount it:
[telesto] (~) >>> umount /var/backup
[telesto] (~) >>> df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/telesto--vg-root 18G 1.5G 15G 9% /
udev 989M 4.0K 989M 1% /dev
tmpfs 200M 276K 200M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 998M 0 998M 0% /run/shm
/dev/mapper/data-media 2.0G 33M 2.0G 2% /var/media
/dev/sda1 228M 54M 163M 25% /boot
/dev/mapper/data-nfs 4.8G 10M 4.6G 1% /var/nfs
This is where we need that block number we saved from earlier. When you are resizing an ext3 filesystem to a specific size (instead of all available space) you need to specify the number of blocks. You can specify the size in MB,GB, etc but we already saves that block number so we’ll use that.
[telesto] (~) >>> resize2fs /dev/data/backup 1310720
resize2fs 1.42 (29-Nov-2011)
Resizing the filesystem on /dev/data/backup to 1310720 (4k) blocks.
The filesystem on /dev/data/backup is now 1310720 blocks long.
With our filesystem size now reduced we need to use lvreduce to shrink the logical volume as well. Note that this is a destructive process and you will be prompted to acknowledge this fact. Since we have not put any data on this filesystem we can safely ignore the warning
[telesto] (~) >>> lvreduce -L5G /dev/data/backup
WARNING: Reducing active logical volume to 5.00 GiB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce backup? [y/n]: y
Reducing logical volume backup to 5.00 GiB
Logical volume backup successfully resized
With all that done we can now remount the logical volume
[telesto] (~) >>> mount /dev/data/backup /var/backup
[telesto] (~) >>> df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/telesto--vg-root 18G 1.5G 15G 9% /
udev 989M 4.0K 989M 1% /dev
tmpfs 200M 276K 200M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 998M 0 998M 0% /run/shm
/dev/mapper/data-media 2.0G 33M 2.0G 2% /var/media
/dev/sda1 228M 54M 163M 25% /boot
/dev/mapper/data-nfs 4.8G 10M 4.6G 1% /var/nfs
/dev/mapper/data-backup 5.0G 139M 4.6G 3% /var/backup
That completes part 2 of our Introduction to LVM series. In the next part of the series we will learn how to setup LVM and software Raid.