LVM is an implementation of a logical volume manager for the Linux kernel. The biggest advantage is that LVM provides the ability to make a snapshot of any logical volume.
In a production environment many users access the same file (file is open) or database. Suppose you start backup process when a file is open, you will not get correct or updated copy of file i.e. inconsistent backup (see accurate definition of inconsistent backup).
Read-only partition – to avoid inconsistent backup
You need to mount partition as read only, so that no one can make changes to file and make a backup:
# umount /home
# mount -o ro /home
# tar -cvf /dev/st0 /home
# umount /home
# mount -o rw /home
As you see, the draw back is service remains unavailable during backup time to all end users. If you are using database then shutdown database server and make a backup.
Logical Volume Manager snapshot to avoid inconsistent backup
This solution will only work if you have created the partition with LVM. A snapshot volume is a special type of volume that presents all the data that was in the volume at the time the snapshot was created. This means you can back up that volume without having to worry about data being changed while the backup is going on, and you don’t have to take the database volume offline while the backup is taking place.
# lvcreate -L1000M -s -n dbbackup /dev/ops/databases
lvcreate -- WARNING: the snapshot must be disabled if it gets full lvcreate -- INFO: using default snapshot chunk size of 64 KB for "/dev/ops/dbbackup" lvcreate -- doing automatic backup of "ops" lvcreate -- logical volume "/dev/ops/dbbackup" successfully created
Create a mount-point and mount the volume:
# mkdir /mnt/ops/dbbackup
# mount /dev/ops/dbbackup /mnt/ops/dbbackup
mount: block device /dev/ops/dbbackup is write-protected, mounting read-only
Do the backup
# tar -cf /dev/st0 /mnt/ops/dbbackup
Now remove it:
# umount /mnt/ops/dbbackup
# lvremove /dev/ops/databases
Please note that LVM snapshots cannot be used with non-LVM filesystems i.e. you need LVM partitions. You can also use third party
commercial proprietary (see below for discussion) or GPL backup solutions/software.
MySQL Backup: Using LVM File System Snapshot
Login to your MySQL server:
# mysql -u root -p
At mysql prompt type the following command to closes all open tables and locks all tables for all databases with a read lock until you explicitly release the lock by executing UNLOCK TABLES. This is very convenient way to get backups if you have a file system such as Veritas or Linux LVM or FreeBD UFS that can take snapshots in time.
mysql> flush tables with read lock;
mysql> flush logs;
Now type the following command (assuming that your MySQL DB is on /dev/vg01/mysql):
# lvcreate --snapshot –-size=1000M --name=backup /dev/vg01/mysql
Again, login to mysql:
# mysql -u root -p
Type the following to release the lock:
mysql> unlock tables;
Now, move backup to tape or other server:
# mkdir -p /mnt/mysql
# mount -o ro /dev/vg01/backup /mnt/mysql
# cd /mnt/mysql
# tar czvf mysql.$(date +"%m-%d%-%Y).tar.gz mysql
# umount /mnt/tmp
# lvremove -f /dev/vg01/backup
If you are using a Veritas file system, you can make a backup like this (quoting from the official MySQL documentation):
Login to mysql and lock the tables:
mysql> FLUSH TABLES WITH READ LOCK;
Type the following at a shell prompt
# mount vxfs snapshot
Now UNLOCK TABLES:
mysql> UNLOCK TABLES;
Copy files from the snapshot and unmount the snapshot.