Chris Tyler - Fedora Linux

# umount /dev/main/multimedia

Next, run a filesystem check to verify the integrity of the filesystem. This is required in order to prevent data loss that may occur if there is data near the end of the filesystem (this is the area that will be freed up by shrinking) and that data is not properly accounted for in the filesystem tables:

# fsck -f /dev/main/multimedia

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/multimedia: 11/117248 files (9.1% non-contiguous), 8043/262144 blocks

Now use resize2fs to reduce the size of the filesystem:

# resize2fs /dev/main/multimedia 740M

resize2fs 1.38 (30-Jun-2005)

Resizing the filesystem on /dev/main/multimedia to 189440 (4k) blocks.

The filesystem on /dev/main/multimedia is now 189440 blocks long.

Note that resize2fs expects the size to be the second argument (there is no --size option as there is with the LVM commands).

The LVM commands accept sizes containing decimals (such as 1.2G), but resize2fs does not; use the next smaller unit to eliminate the decimal point (1200M).

Both the filesystem commands and the LVM commands round off sizes to the closest multiple of their internal allocation units. This means that resize2fs and lvreduce may interpret a size such as 750M slightly differently. In order to avoid the potential disaster of resizing the LV to be smaller than the filesystem, always resize the filesystem so that it is slightly smaller than the planned LV size, resize the LV, and then grow the filesystem to exactly fill the LV. In this case, I'm resizing the filesystem to 740 MB and will resize the LV to 750 MB.

Now that the filesystem has been resized, you can shrink the logical volume:

# lvreduce /dev/main/multimedia --size 750M

Rounding up size to full physical extent 752.00 MB

WARNING: Reducing active logical volume to 752.00 MB

THIS MAY DESTROY YOUR DATA (filesystem etc.)

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

Reducing logical volume multimedia to 752.00 MB

Logical volume multimedia successfully resized

Finally, grow the filesystem to completely fill the logical volume:

# resize2fs /dev/main/multimedia

resize2fs 1.38 (30-Jun-2005)

Resizing the filesystem on /dev/main/multimedia to 192512 (4k) blocks.

The filesystem on /dev/main/multimedia is now 192512 blocks long.

The lvcreate command will create a new volume:

# lvcreate main --name survey --size 5G

Logical volume "survey" created

Next, add a filesystem:

# mkfs -t ext3 -L survey -E resize= 20G /dev/main/survey

mke2fs 1.38 (30-Jun-2005)

Filesystem label=survey

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

655360 inodes, 1310720 blocks

65536 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=8388608

40 block groups

32768 blocks per group, 32768 fragments per group

16384 inodes per group

Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736

Writing inode tables: done

Creating journal (32768 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 36 mounts or

180 days, whichever comes first. Use tune2fs -c or -i to override.

The -t ext3 option specifies the filesystem type, -L survey specifies a optional filesystem volume label (to identify the contents), and -E resize= 20G (also optional) configures a block group descriptor table large enough that the filesystem can be grown up to 20 GB while mounted. In this case, 20 GB is four times the initial size of the filesystem; use whatever upper limit seems reasonable for your application (the table will take roughly 4 KB of space for each gigabyte in the filesystem maximum size, so the overhead is minimal).

You can now mount the filesystem and use it. Here I'll use /usr/lib/survey as the mount point:

# mkdir /usr/lib/survey

# mount /dev/main/survey /usr/lib/survey

To configure the Fedora system to mount this filesystem every time it is booted, add an entry to the file /etc/fstab :

/dev/main/root / ext3 defaults 1 1

LABEL=/boot /boot ext3 defaults 1 2

devpts /dev/pts devpts gid=5,mode=620 0 0

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).

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