Splitting a volume group

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# 13.7. Splitting a volume group

There is a new group of users "design" to add to the system. One way of dealing with this is to create a new volume group to hold their data. There are no new disks but there is plenty of free space on the existing disks that can be reallocated.

## 13.7.1. Determine free space

    # pvscan
    pvscan -- reading all physical volumes (this may take a while...)
    pvscan -- ACTIVE   PV "/dev/sda"  of VG "dev"   [1.95 GB / 0 free]
    pvscan -- ACTIVE   PV "/dev/sdb"  of VG "sales" [1.95 GB / 1.27 GB free]
    pvscan -- ACTIVE   PV "/dev/sdc"  of VG "ops"   [1.95 GB / 564 MB free]
    pvscan -- ACTIVE   PV "/dev/sdd"  of VG "dev"   [1.95 GB / 0 free]
    pvscan -- ACTIVE   PV "/dev/sde"  of VG "ops"   [1.95 GB / 1.9 GB free]
    pvscan -- ACTIVE   PV "/dev/sdf"  of VG "dev"   [1.95 GB / 1.33 GB free]
    pvscan -- ACTIVE   PV "/dev/sdg1" of VG "ops"   [996 MB / 432 MB free]
    pvscan -- ACTIVE   PV "/dev/sdg2" of VG "dev"   [996 MB / 632 MB free]
    pvscan -- total: 8 [13.67 GB] / in use: 8 [13.67 GB] / in no VG: 0 [0]

We decide to reallocate /dev/sdg1 and /dev/sdg2 to design so first we have to move the physical extents into the free areas of the other volumes (in this case /dev/sdf for volume group dev and /dev/sde for volume group ops).

## 13.7.2. Move data off the disks to be used

Some space is still used on the chosen volumes so it is necessary to move that used space off onto some others.

Move all the used physical extents from /dev/sdg1 to /dev/sde and from /dev/sdg2 to /dev/sdf

    # pvmove /dev/sdg1 /dev/sde
    pvmove -- moving physical extents in active volume group "ops"
    pvmove -- WARNING: moving of active logical volumes may cause data loss!
    pvmove -- do you want to continue? [y/n] y
    pvmove -- doing automatic backup of volume group "ops"
    pvmove -- 141 extents of physical volume "/dev/sdg1" successfully moved

    # pvmove /dev/sdg2 /dev/sdf
    pvmove -- moving physical extents in active volume group "dev"
    pvmove -- WARNING: moving of active logical volumes may cause data loss!
    pvmove -- do you want to continue? [y/n] y
    pvmove -- doing automatic backup of volume group "dev"
    pvmove -- 91 extents of physical volume "/dev/sdg2" successfully moved

## 13.7.3. Create the new volume group

Now, split /dev/sdg2 from dev and add it into a new group called "design". it is possible to do this using vgreduce and vgcreate but the vgsplit command combines the two.

    # vgsplit dev design /dev/sdg2
    vgsplit -- doing automatic backup of volume group "dev"
    vgsplit -- doing automatic backup of volume group "design"
    vgsplit -- volume group "dev" successfully split into "dev" and "design"

## 13.7.4. Remove remaining volume

Next, remove /dev/sdg1 from ops and add it into design.

    # vgreduce ops /dev/sdg1
    vgreduce -- doing automatic backup of volume group "ops"
    vgreduce -- volume group "ops" successfully reduced by physical volume:
    vgreduce -- /dev/sdg1

    # vgextend design /dev/sdg1
    vgextend -- INFO: maximum logical volume size is 255.99 Gigabyte
    vgextend -- doing automatic backup of volume group "design"
    vgextend -- volume group "design" successfully extended

## 13.7.5. Create new logical volume

Now create a logical volume. Rather than allocate all of the available space, leave some spare in case it is needed elsewhere.

    # lvcreate -L750M -n users design
    lvcreate -- rounding up size to physical extent boundary "752 MB"
    lvcreate -- doing automatic backup of "design"
    lvcreate -- logical volume "/dev/design/users" successfully created

## 13.7.6. Make a file system on the volume

    # mke2fs /dev/design/users
    mke2fs 1.18, 11-Nov-1999 for EXT2 FS 0.5b, 95/08/09
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    96384 inodes, 192512 blocks
    9625 blocks (5.00<!-- ) reserved for the super user
    First data block=0
    6 block groups
    32768 blocks per group, 32768 fragments per group
    16064 inodes per group
    Superblock backups stored on blocks:
            32768, 98304, 163840

    Writing inode tables: done
    Writing superblocks and filesystem accounting information: done

## 13.7.7. Mount the new volume

    # mkdir -p /mnt/design/users mount /dev/design/users /mnt/design/users/

It's also a good idea to add an entry for this file system in your /etc/fstab file as follows:

    /dev/design/user
    /mnt/design/users   ext2    defaults        1 2

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