Let to see, step-by-step, a real example of Volume Manager on a CentOS 7 setup.
On the host caldera01 there is an additional disk /dev/sdb we want to use for store a mysql database.
[root@caldera01 ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/os-root xfs 50G 2.1G 48G 5% /
devtmpfs devtmpfs 3.8G 0 3.8G 0% /dev
tmpfs tmpfs 3.8G 0 3.8G 0% /dev/shm
tmpfs tmpfs 3.8G 8.6M 3.8G 1% /run
tmpfs tmpfs 3.8G 0 3.8G 0% /sys/fs/cgroup
/dev/mapper/os-data xfs 175G 256M 175G 1% /data
/dev/sda1 xfs 497M 190M 308M 39% /boot
[root@caldera01 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 232.9G 0 disk
├─sda1 8:1 0 500M 0 part /boot
└─sda2 8:2 0 232.4G 0 part
├─os-swap 253:0 0 7.8G 0 lvm [SWAP]
├─os-root 253:1 0 50G 0 lvm /
└─os-data 253:2 0 174.6G 0 lvm /data
sdb 8:16 0 232.9G 0 disk
└─sdb1 8:17 0 232.9G 0 part
[root@caldera01 ~]# fdisk /dev/sdb
Disk /dev/sdb: 250.1 GB, 250059350016 bytes, 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0003b431
Device Boot Start End Blocks Id System
/dev/sdb1 2048 488397167 244197560 8e Linux LVM
Create a LVM layout
[root@caldera01 ~]# pvcreate /dev/sdb1
[root@caldera01 ~]# vgcreate vgdb /dev/sdb1
[root@caldera01 ~]# lvcreate -l 100%FREE -n lvol1 vgdb
[root@caldera01 ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 os lvm2 a-- 232.39g 0
/dev/sdb1 vgdb lvm2 a-- 232.88g 0
[root@caldera01 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
os 1 3 0 wz--n- 232.39g 0
vgdb 1 1 0 wz--n- 232.88g 0
[root@caldera01 ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
data os -wi-ao---- 174.63g
root os -wi-ao---- 50.00g
swap os -wi-ao---- 7.77g
lvol1 vgdb -wi-ao---- 232.88g
Make an ext3 file system on the logical volume and mount the partition under a /db directory
[root@caldera01 ~]# mkfs -t ext3 /dev/vgdb/lvol1
[root@caldera01 ~]# mkdir /db
[root@caldera01 ~]# mount /dev/sdb1 /db
Install a mysql database on the new filesystem
[root@caldera01 ~]# sudo rpm -Uvh http://dev.mysql.com/get/mysql-community-release-el7-5.noarch.rpm
[root@caldera01 ~]# yum install -y mysql-server
[root@caldera01 ~]# vi /etc/my.cnf
[mysqld]
...
datadir=/db/mysql
...
[root@caldera01 ~]# systemctl start mysqld
[root@caldera01 ~]# systemctl status mysqld
[root@caldera01 ~]# systemctl enable mysqld
From GitHub, install a sample database with an integrated test suite, used to test your applications and database servers
[root@caldera01 ~]# yum install -y git
[root@caldera01 ~]# git clone https://github.com/datacharmer/test_db.git
[root@caldera01 ~]# cd /db/test_db
Load the test database
[root@caldera01 ~]# mysql < employees.sql
If you want to install with two large partitioned tables, alternatively, run
[root@caldera01 ~]# mysql < employees_partitioned.sql
Run the test suite
[root@caldera01 ~]# mysql -t < test_employees_md5.sql
+----------------------+
| INFO |
+----------------------+
| TESTING INSTALLATION |
+----------------------+
+--------------+------------------+----------------------------------+
| table_name | expected_records | expected_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+------------------+----------------------------------+
| table_name | found_records | found_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+---------------+-----------+
| table_name | records_match | crc_match |
+--------------+---------------+-----------+
| employees | OK | ok |
| departments | OK | ok |
| dept_manager | OK | ok |
| dept_emp | OK | ok |
| titles | OK | ok |
| salaries | OK | ok |
+--------------+---------------+-----------+
We want to add 2 additional LUNs via iSCSI protocol to the LVM layout. The iSCSI makes the system able to see the external LUNs as additional disks, called /dev/sdc and /dev/sdd
Each additional disk is of 232.9G
[root@caldera01 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 232.9G 0 disk
├─sda1 8:1 0 500M 0 part /boot
└─sda2 8:2 0 232.4G 0 part
├─os-swap 253:0 0 7.8G 0 lvm [SWAP]
├─os-root 253:1 0 50G 0 lvm /
└─os-data 253:2 0 174.6G 0 lvm /data
sdb 8:16 0 232.9G 0 disk
└─sdb1 8:17 0 232.9G 0 part
└─vgdb-lvol1 253:4 0 232.9G 0 lvm /db
sdc 8:32 0 232.9G 0 disk
sdd 8:48 0 232.9G 0 disk
Now let's to extend the LV lvol1 by using the 2 additional LUNs
[root@caldera01 ~]# pvcreate -f /dev/sdc
Wiping iso9660 signature on /dev/sdc.
Wiping dos signature on /dev/sdc.
Physical volume "/dev/sdc" successfully created
[root@caldera01 ~]# pvcreate -f /dev/sdd
Wiping dos signature on /dev/sdd.
Physical volume "/dev/sdd" successfully created
[root@caldera01 ~]# pvscan
PV /dev/sda2 VG os lvm2 [232.39 GiB / 0 free]
PV /dev/sdb1 VG vgdb lvm2 [232.88 GiB / 0 free]
PV /dev/sdc lvm2 [232.89 GiB]
PV /dev/sdd lvm2 [232.89 GiB]
[root@caldera01 ~]# vgextend vgdb /dev/sdc /dev/sdd
Volume group "vgdb" successfully extended
[root@caldera01 ~]# vgscan
Reading all physical volumes. This may take a while...
Found volume group "os" using metadata type lvm2
Found volume group "vgdb" using metadata type lvm2
[root@caldera01 ~]# vgdisplay vgdb
--- Volume group ---
VG Name vgdb
System ID
Format lvm2
Metadata Areas 3
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 3
Act PV 3
VG Size 698.64 GiB
PE Size 4.00 MiB
Total PE 178852
Alloc PE / Size 59618 / 232.88 GiB
Free PE / Size 119234 / 465.76 GiB
VG UUID O557zn-CcSI-1Ec4-LryC-uqi8-B42R-pYTHKU
[root@caldera01 ~]# lvscan
ACTIVE '/dev/os/root' [50.00 GiB] inherit
ACTIVE '/dev/os/data' [174.63 GiB] inherit
ACTIVE '/dev/os/swap' [7.77 GiB] inherit
ACTIVE '/dev/vgdb/lvol1' [232.88 GiB] inherit
[root@caldera01 ~]# lvextend -L +400G /dev/vgdb/lvol1
Size of logical volume vgdb/lvol1 changed from 232.88 GiB (59618 extents) to 632.88 GiB (162018 extents).
Logical volume lvol1 successfully resized
[root@caldera01 ~]#
[root@caldera01 ~]# lvscan
ACTIVE '/dev/os/root' [50.00 GiB] inherit
ACTIVE '/dev/os/data' [174.63 GiB] inherit
ACTIVE '/dev/os/swap' [7.77 GiB] inherit
ACTIVE '/dev/vgdb/lvol1' [632.88 GiB] inherit
Now the LV successfully increased its size by 632G but the file system still is 232G
[root@caldera01 ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/os-root xfs 50G 2.1G 48G 5% /
devtmpfs devtmpfs 3.8G 0 3.8G 0% /dev
tmpfs tmpfs 3.8G 0 3.8G 0% /dev/shm
tmpfs tmpfs 3.8G 8.6M 3.8G 1% /run
tmpfs tmpfs 3.8G 0 3.8G 0% /sys/fs/cgroup
/dev/mapper/os-data xfs 175G 256M 175G 1% /data
/dev/sda1 xfs 497M 190M 308M 39% /boot
/dev/mapper/vgdb-lvol1 ext3 230G 642M 217G 1% /db
Extend the file system without umount it
[root@caldera01 ~]# resize2fs -p /dev/vgdb/lvol1
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/vgdb/lvol1 is mounted on /db; on-line resizing required
old_desc_blocks = 15, new_desc_blocks = 40
The filesystem on /dev/vgdb/lvol1 is now 165906432 blocks long.
Let's check our data file
[root@caldera01 ~]# cd /db/test_db
[root@caldera01 ~]# mysql -t < test_employees_md5.sql
+----------------------+
| INFO |
+----------------------+
| TESTING INSTALLATION |
+----------------------+
+--------------+------------------+----------------------------------+
| table_name | expected_records | expected_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+------------------+----------------------------------+
| table_name | found_records | found_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+---------------+-----------+
| table_name | records_match | crc_match |
+--------------+---------------+-----------+
| employees | OK | ok |
| departments | OK | ok |
| dept_manager | OK | ok |
| dept_emp | OK | ok |
| titles | OK | ok |
| salaries | OK | ok |
+--------------+---------------+-----------+
Our data is safe! Now we want to resize the logical volume to use only 1 LUN instead of 2 LUNs as we made before. Firt of all, shutdown any service or application that is using the logical volume we want to resize. In our case, we have to stop the MySQL database running on the volume
[root@caldera01 test_db]# systemctl stop mysql
[root@caldera01 test_db]# systemctl status mysql
mysqld.service - MySQL Community Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled)
Active: inactive (dead) since Thu 2015-10-22 12:13:28 CEST; 2min 12s ago
Main PID: 15388 (code=exited, status=0/SUCCESS)
Make a backup of ALL yuor data present on the volume
[root@caldera01 test_db]# tar cvf data_backup.tar *
[root@caldera01 test_db]# gzip data_backup.tar
[root@caldera01 test_db]# mv data_backup.tar /data_backup_folder
Umount the LV
[root@caldera01 ~]# umount /db
Then check for the file-system error (Must pass in every 5 steps of file-system check if not there might be some issue with your file-system)
[root@caldera01 /]# e2fsck -ff /dev/vgdb/lvol1
e2fsck 1.42.9 (28-Dec-2013)
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/vgdb/lvol1: 403/41484288 files (10.9% non-contiguous), 2803302/165906432 blocks
Now let's to resize the file system. Since we want to remove the last LUN, we have to calculate the final size of the file system by summing its original size /dev/sdb1 to the size of the first added LUN /dev/sdc. We have /dev/sdb1 Total PE 59618 + /dev/sdc Total PE 59617 = Total PE 119235. Total size, expressed in Megabyte are 4 x 119235 = 476940 MB
[root@caldera01 ~]# pvdisplay
--- Physical volume ---
PV Name /dev/sdb1
VG Name vgdb
PV Size 232.88 GiB / not usable 2.18 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 59618
Free PE 0
Allocated PE 59618
PV UUID mymhL6-Ta6m-cx3V-LjKM-Zo2T-K7Xj-MI1jb3
--- Physical volume ---
PV Name /dev/sdc
VG Name vgdb
PV Size 232.89 GiB / not usable 7.18 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 59617
Free PE 0
Allocated PE 59617
PV UUID 0dIQWO-jjaa-zgl3-1o8E-8kGR-4xjc-BxPmwO
--- Physical volume ---
PV Name /dev/sdd
VG Name vgdb
PV Size 232.89 GiB / not usable 7.18 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 59617
Free PE 16834
Allocated PE 42783
PV UUID Df0M7R-6KDB-TUeZ-l1Gw-2r5J-ci4c-MsyNw4
[root@caldera01 ~]# fsadm -e -y resize /dev/vgdb/lvol1 476940M
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/mapper/vgdb-lvol1 to 122096640 (4k) blocks.
The filesystem on /dev/mapper/vgdb-lvol1 is now 122096640 blocks long.
Reduce the Logical Volume and remove the last LUN from the Volume Group
[root@caldera01 ~]# lvreduce -L 476940M /dev/vgdb/lvol1
WARNING: Reducing active logical volume to 465.76 GiB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce lvol1? [y/n]: y
Size of logical volume vgdb/lvol1 changed from 632.88 GiB (162018 extents) to 465.76 GiB (119235 extents).
Logical volume lvol1 successfully resized
[root@caldera01 ~]# vgreduce vgdb /dev/sdd
Removed "/dev/sdd" from volume group "vgdb"
[root@caldera01 ~]#
Remove the physical volume
[root@caldera01 ~]# pvremove /dev/sdd
Labels on physical volume "/dev/sdd" successfully wiped
[root@caldera01 ~]#
And check again the file system and mount back it
[root@caldera01 ~]# e2fsck -ff /dev/vgdb/lvol1
e2fsck 1.42.9 (28-Dec-2013)
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/vgdb/lvol1: 403/30531584 files (10.9% non-contiguous), 2116084/122096640 blocks
[root@caldera01 ~]#
[root@caldera01 ~]# mount /dev/vgdb/lvol1 /db
[root@caldera01 ~]# df -Th /db
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/vgdb-lvol1 ext3 459G 653M 439G 1% /db
[root@caldera01 ~]#
Start the mysql service and check for data integrity
[root@caldera01 ~]# systemctl start mysqld
[root@caldera01 ~]# cd /db/test_db/
[root@caldera01 test_db]# mysql -t < test_employees_md5.sql
+----------------------+
| INFO |
+----------------------+
| TESTING INSTALLATION |
+----------------------+
+--------------+------------------+----------------------------------+
| table_name | expected_records | expected_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+------------------+----------------------------------+
| table_name | found_records | found_crc |
+--------------+------------------+----------------------------------+
| employees | 300024 | 4ec56ab5ba37218d187cf6ab09ce1aa1 |
| departments | 9 | d1af5e170d2d1591d776d5638d71fc5f |
| dept_manager | 24 | 8720e2f0853ac9096b689c14664f847e |
| dept_emp | 331603 | ccf6fe516f990bdaa49713fc478701b7 |
| titles | 443308 | bfa016c472df68e70a03facafa1bc0a8 |
| salaries | 2844047 | fd220654e95aea1b169624ffe3fca934 |
+--------------+------------------+----------------------------------+
+--------------+---------------+-----------+
| table_name | records_match | crc_match |
+--------------+---------------+-----------+
| employees | OK | ok |
| departments | OK | ok |
| dept_manager | OK | ok |
| dept_emp | OK | ok |
| titles | OK | ok |
| salaries | OK | ok |
+--------------+---------------+-----------+
+------------------+
| computation_time |
+------------------+
| 00:00:14 |
+------------------+
+---------+--------+
| summary | result |
+---------+--------+
| CRC | OK |
| count | OK |
+---------+--------+