Monday, June 8, 2009

Howto: Setup LVM on 3 SCSI Disk

This setup has three SCSI disks that will be put into a logical volume using LVM. The disks are at /dev/sda, /dev/sdb, and /dev/sdc. This can serve as a sample for setting up LVM on three storage devices.

Before you can use a disk in a volume group you will have to prepare it:

Run pvcreate on the disks

# pvcreate /dev/sda
# pvcreate /dev/sdb
# pvcreate /dev/sdc

This creates a volume group descriptor area (VGDA) at the start of the disks.

Setup a Volume Group:
1.Create a volume group
# vgcreate my_volume_group /dev/sda /dev/sdb /dev/sdc/

2. Run vgdisplay to verify volume group

# vgdisplay
# vgdisplay
--- Volume Group ---
VG Name my_volume_group
VG Access read/write
VG Status available/resizable
VG # 1
MAX LV 256
Cur LV 0
Open LV 0
MAX LV Size 255.99 GB
Max PV 256
Cur PV 3
Act PV 3
VG Size 1.45 GB
PE Size 4 MB
Total PE 372
Alloc PE / Size 0 / 0
Free PE / Size 372/ 1.45 GB
VG UUID nP2PY5-5TOS-hLx0-FDu0-2a6N-f37x-0BME0Y

The most important things to verify are that the first three items are correct and that the VG Size item is the proper size for the amount of space in all four of your disks.

Creating the Logical Volume

If the volume group looks correct, it is time to create a logical volume on top of the volume group.

You can make the logical volume any size you like. (It is similar to a partition on a non LVM setup.) For this example we will create just a single logical volume of size 1GB on the volume group. We will not use striping because it is not currently possible to add a disk to a stripe set after the logical volume is created.

# lvcreate -L1G -nmy_logical_volume my_volume_group
lvcreate -- doing automatic backup of "my_volume_group"
lvcreate -- logical volume "/dev/my_volume_group/my_logical_volume" successfully created

Create the File System

Create an ext2 file system on the logical volume

# mke2fs /dev/my_volume_group/my_logical_volume
mke2fs 1.19, 13-Jul-2000 for EXT2 FS 0.5b, 95/08/09
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
131072 inodes, 262144 blocks
13107 blocks (5.00%) reserved for the super user
First data block=0
9 block groups
32768 blocks per group, 32768 fragments per group
16384 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376

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

Test the File System

Mount the logical volume and check to make sure everything looks correct

# mount /dev/my_volume_group/my_logical_volume /mnt
# df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/hda1 1311552 628824 616104 51% /
1040132 20 987276 0% /mnt

If everything went well, you should now have a logical volume with and ext2 file system mounted at /mnt.

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