Fedora Linux

tmpfs /dev/shm tmpfs defaults 0 0
proc /proc proc defaults 0 0
sysfs /sys sysfs defaults 0 0
/dev/main/swap swap swap defaults 0 0
/dev/main/home /home ext3 defaults 1 2
/dev/main/multimedia /tmp/media ext3 defaults 1 2
/dev/main/survey /usr/lib/survey ext3 defaults 1 2

The new line (highlighted in bold) contains the filesystem block device, the mount point, the filesystem type, any mount options ( defaults specifies the default options, which include mounting the filesystem at boot time), whether the filesystem should be backed up ( 1 meaning yes ), and the fsck sequence number ( 2 is for filesystems that should be checked but that are not the root filesystem).

6.1.1.3.6. Creating a snapshot logical volume

The lvcreate command is also used to create snapshot volumes:

# lvcreate -s /dev/main/survey --name survey-snap --size 500M
Logical volume 'survey-snap' created

The -s option indicates that this is a snapshot LV. Specify the origin LV as the first positional argument, and use the --name and --size options as you would for a regular lvcreate command. However, the value given for the --size option must be the amount of space allocated for tracking the differences between the origin LV and the snapshot LV.

Once the snapshot has been created, it can be mounted and used:

# mkdir /usr/lib/survey-snap
# mount /dev/main/survey-snap /usr/lib/survey- snap

To have the snapshot automatically mounted when the system is booted, edit the file /etc/fstab in the same way that you would for a regular filesystem.

To see how much of a snapshot's storage is in use, use lvs or lvdisplay :

# lvs
LV VG Attr LSize Origin Snap% Move Log Copy%
home main -wi-ao 1.00G
multimedia main -wi-a- 752.00M
root main -wi-ao 9.77G
survey main owi-ao 5.00G
survey-snap main swi-ao 500.00M survey 8.27
swap main -wi-ao 1.00G
# lvdisplay /dev/main/survey- snap --- Logical volume ---
LV Name /dev/main/survey-snap
VG Name main
LV UUID IbG5RS-Tcle-kzrV-Ga9b-Jsgx-3MY6-iEXBGG
LV Write Access read/write
LV snapshot status active destination for /dev/main/survey
LV Status available
# open 1
LV Size 5.00 GB
Current LE 1280
COW-table size 500.00 MB
COW-table LE 125
Allocated to snapshot 8.27%
Snapshot chunk size 8.00 KB
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:7

In this case, 8.27% of the snapshot storage has been used, or about 41 MB. If this approaches 100%, you can grow the snapshot LV using lvextend in the same way that a regular LV is grown.

6.1.1.3.7. Removing a logical volume

To remove a logical volume, unmount it, and then use lvremove :

# umount /usr/lib/survey-snap
# lvremove /dev/main/survey- snap
Do you really want to remove active logical volume 'survey-snap'? [y/n]: y
Logical volume 'survey-snap' successfully removed

Removing an LV is irreversible, so be sure that you're not deleting any important data.

6.1.1.3.8. Adding a partition

To set up a partition for use as a physical volume, use the pvcreate command to write the LVM disk label, making the partition into a physical volume:

# pvcreate /dev/sde1
Physical volume '/dev/sde1' successfully created

If the disk is not partitioned, you can use fdisk or (more easily) parted to create a partition before running pvcreate.