Chris Tyler - Fedora Linux

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.

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.

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 .

These commands create a single partition that fills the entire disk /dev/sde :

# parted /dev/sde mklabel msdos# parted -- /dev/sde mkpart primary ext2 1 -1

In this case, the partition will be /dev/sde1 .

You can then add that PV to an existing volume group:

# vgextend main /dev/sde1

Volume group "main" successfully extended

The vgreduce command is used to reduce the size of a volume group by removing a physical volume. It will fail if any space on the PV is in use:

# vgreduce main /dev/sdb1

Physical volume "/dev/sdb1" still in use

In this case, an attempt to remove /dev/sdb1 from the volume group main failed. To move the data off a PV (assuming that there is sufficient space available on other PVs in the volume group), use the pvmove command:

# pvmove /dev/sde1 /dev/sde1: Moved: 100.0%

Depending on the amount of date to be moved, this operation can take quite a while to run. When it is complete, you can remove the physical volume:

# vgreduce main /dev/sdb1

Removed "/dev/sdb1" from volume group "test"

You can then use that partition for other uses. If you want to erase the LVM disk label, use the pvremove command:

# pvremove /dev/sde1

Labels on physical volume "/dev/sde1" successfully wiped

Some filesystems, such as those containing /var or /etc , may be in use anytime the system is booted normally. This prevents the use of resize2fs to shrink ext2 and ext3 filesystems or to grow them large enough to exceed the block group descriptor table.

To use resize2fs on these filesystems, you must use runlevel s , which is single-user mode. Boot your system, and press the spacebar when the GRUB boot screen appears. Press the A key to append text to the boot line; then type sand press Enter. After a few seconds, a root shell prompt will appear ( sh-3.1# ).

At this shell prompt you can unmount the filesystem, then use fsck , resize2fs , and lvreduce (or lvextend ). For example, to reduce the size of /home to 925 MB:

sh-3.1# umount /home

sh-3.1# fsck -f /dev/main/home

e2fsck 1.38 (30-Jun-2005)

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/main/home: 121/256000 files (2.5% non-contiguous), 12704/262144 blocks

sh-3.1# resize2fs /dev/main/home 900M

resize2fs 1.38 (30-Jun-2005)

Resizing the filesystem on /dev/main/home to 230400 (4k) blocks.

The filesystem on /dev/main/home is now 229376 blocks long.

sh-3.1# lvreduce /dev/main/home --size 950 M

Rounding up size to full physical extent 952.00 MB

WARNING: Reducing active logical volume to 952.00 MB

THIS MAY DESTROY YOUR DATA (filesystem etc.)

Do you really want to reduce home? [y/n]: y

Reducing logical volume home to 952.00 MB

Logical volume home successfully resized

sh-3.1# resize2fs /dev/main/home

resize2fs 1.38 (30-Jun-2005)

Resizing the filesystem on /dev/main/home to 243712 (4k) blocks.

The filesystem on /dev/main/home is now 243712 blocks long.

The warning message displayed by lvreduce is accurate: if you set the logical volume size smaller than the filesystem size, you will lose data! Be extremely careful when resizing volumes; it's a good idea to back up your data first.

If your system has the default Volume Group and Logical Volume names, substitute the correct name (such as /dev/VolGroup00/LogVol00 ) for /dev/main/home . The problem is that it's hard to keep the logical volume names straightwhich is why I recommend using more meaningful names.