3.3 Creating an LVM Volume Group and Logical Volume

After you have installed MySQL, you are ready to set up the LVM volume group and logical volume where you will store a MySQL database. Sample values are used in the procedures in this section to help you understand what is required at each step. The overview provides only the Linux commands that you need to create and prepare the volume group for use by MySQL. The detailed description provides more information about the process, including the syntax and sample commands.

3.3.1 Sample Values

The procedures in this section uses the following parameters. Ensure that you replace the sample values with your values. The first node in the cluster is where you configure MySQL and the cluster resource.

Parameter	Sample Value
LVM physical volume	/dev/sdd
LVM volume group name	mysqlvg
LVM logical volume	msqllv
File system type	ext3 This is the file system type that you make on the LVM logical volume, such as ext2, ext3, reiserfs, or xfs.
Logical volume path	/dev/mysqlvg/mysqllv
Mount point for the logical volume	/mnt/mysql
Default MySQL root path	/var/lib/mysql
New MySQL root path	/mnt/mysql/var/lib/mysql

3.3.2 Setting Up the VG and LV (Overview)

You can create the volume group and logical volume by issuing the following LVM commands as the root user on the cluster node. This overview of the process uses the sample values. Ensure that you substitute your own values in the commands. For details, see Section 3.3.3, Setting up the VG and LV (Detailed).

Command Action	Command
1. Create the LVM physical volume.	pvcreate /dev/sdd
2. Create the clustered LVM volume group.	vgcreate -c y mysqlvg /dev/sdd
3. Activate the volume group exclusively on the node.	vgchange -a ey mysqlvg
4. Create the LVM logical volume.	lvcreate -n mysqllv -L size mysqlvg
5. Add a file system to the LVM logical volume.	mkfs -t ext3 /dev/mysqlvg/mysqllv [fs_options]
6. Create a mount point for the logical volume.	mkdir /mnt/mysql You must also create this path on each node in the cluster.
7. Mount the LVM logical volume.	mount -t ext3 /dev/mysqlvg/mysqllv /mnt/mysql
8. Create the directory structure for the MySQL database files on the mounted logical volume.	cd /mnt/mysql mkdir /mnt/mysql/var mkdir /mnt/mysql/var/lib mkdir /mnt/mysql/var/lib/mysql
9. Modify the file ownership of the mount point and subdirectories.	chown -R mysql:mysql /mnt/mysql
10. Unmount the LVM logical volume.	cd / unmount /mnt/mysql
10. Deactivate the LVM logical volume.	vgchange -a n mysqlvg

3.3.3 Setting up the VG and LV (Detailed)

For detailed instructions, use the following procedure to create the LVM volume group and logical volume:

Log in as the Linux root user to the first node of the cluster, then open a terminal console.
In NSSMU, initialize the SAN device that you want to use for the MySQL database, but do not mark it as shareable for clustering:
1. At the console prompt, launch NSSMU by entering:
```
nssmu
```
2. Select Devices, then press Enter.
3. In the Devices list, select the unpartitioned device that you want to use, then press F3 to initialize it.
4. Read the advisory, then press Y to confirm that you want to initialize the device.
5. Specify the Master Boot Record (MBR) type as DOS or GPT, then press Enter.
  
  Typically, you use DOS format for devices up to 2 TB. You use GPT for devices greater than 2 TB.
6. Verify that the device is initialized and that it is unshared (that is, Shareable for Clustering is set to No).
7. Exit NSSMU to return to the command prompt.

Create an LVM physical volume on the device (such as /dev/sdd) by entering:

pvcreate <device>

For example:

pvcreate /dev/sdd
  No physical volume label read from /dev/sdd
  Physical volume "/dev/sdd" successfully created

Create an LVM volume group (such as mysqlvg) on the physical volume by entering:
```
vgcreate -c y <vg_name> <device>
```
For example:
```
vgcreate -c y "mysqlvg" /dev/sdd
  Clustered volume group "mysqlvg" successfully created
```
The volume group is automatically activated.
Activate the volume group exclusively on the current server by entering:
```
vgchange -a ey <vg_name>
```
The -a option activates the volume. The ey parameter specifies the values exclusively and yes.

For example:
```
vgchange -a ey mysqlvg
```

View information about the volume group by using the vgdisplay command:

vgdisplay <vg_name>

Notice that 4 MB of the device are used for the volume group’s Physical Extent (PE) table. You must consider this reduction in available space on the volume group when you specify the size of the LVM logical volume in the next step (Step 7).

For example:

vgdisplay mysqlvg
  --- Volume group ---
  VG Name               mysqlvg
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               508.00 MB
  PE Size               4.00 MB
  Total PE              127
  Alloc PE / Size       0 / 0   
  Free  PE / Size       127 / 508.00 MB
  VG UUID               rqyAd3-U2dg-HYLw-0SyN-loO7-jBH3-qHvySe

Create an LVM logical volume (such as mysqllv) on the volume group by entering:
```
lvcreate -n <lv_name> -L size <vg_name>
```
Specify the logical volume name, size, and the name of the volume group where you want to create it. The size is specified in megabytes by default.

The logical volume full path name is /dev/<vg_name>/<lv_name>.

For example:
```
lvcreate -n "mysqllv" -L 500 "mysqlvg"
  Logical volume "mysqllv" created
```
This volume’s full path name is /dev/mysqlvg/mysqllv.

View information about the logical volume by entering:

lvdisplay -v <lv_path_name>

For example:

lvdisplay -v /dev/mysqlvg/mysqllv
    Using logical volume(s) on command line
  --- Logical volume ---
  LV Name                /dev/mysqlvg/mysqllv
  VG Name                mysqlvg
  LV UUID                nIfsMp-alRR-i4Lw-Wwdt-v5io-2hDN-qrWTLH
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                500.00 MB
  Current LE             125
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     1024
  Block device           253:1

Create a file system (such as Ext2, Ext3, ReiserFS, or XFS) on the LVM logical volume by entering:

mkfs -t <fs_type> <lv_path_name> [fs_options]

You can specify file system options according to the type of file system you are making. For information, see the mkfs(8) man page and the related man page for the file system type, such as mkfs.ext2(8), mkfs.ext3(8), mkfs.reiserfs(8), or mkfs.xfs(8).

For example:

mkfs -t ext3 /dev/mysqlvg/mysqllv
  mke2fs 1.41.9 (22-Aug-2009)
  Filesystem label=
  OS type: Linux
  Block size=1024 (log=0)
  Fragment size=1024 (log=0)
  128016 inodes, 512000 blocks
  25600 blocks (5.00%) reserved for the super user
  First data block=1
  Maximum filesystem blocks=67633152
  63 block groups
  8192 blocks per group, 8192 fragments per group
  2032 inodes per group
  Superblock backups stored on blocks: 
    8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
  Writing inode tables: done                            
  Creating journal (8192 blocks): done
  Writing superblocks and filesystem accounting information: done

  This filesystem will be automatically checked every 29 mounts or
    180 days, whichever comes first.  Use tune2fs -c or -i to override.

Create a mount point for the logical volume by entering:
```
mkdir /mnt/mysql
```

Mount the logical volume on the MySQL mount point by entering:

mount -t <fs_type> <lv_path_name> <mount_point>

For example:

mount -t ext3 /dev/mysqlvg/mysqllv /mnt/mysql

Go to the mount point location (/mnt/mysql), then create the /var/lib/mysql subdirectory structure by entering:
```
cd /mnt/mysql
mkdir /mnt/mysql/var
mkdir /mnt/mysql/var/lib
mkdir /mnt/mysql/var/lib/mysql
```
Change the owner and group owner of the /mnt/mysql directory and its contents to use the mysql user and group. Enter the chown command with the recursive (-R) option:
```
cd /mnt
chown -R mysql:mysql mysql
```
Another way to do this is to explicitly specify the directory path:
```
chown -R mysql:mysql /mnt/mysql
```
Continue with Section 3.4, Configuring MySQL on the LVM Logical Volume.