LVM2 Logical Volume Manager 详解（五）--利用快照备份

快照卷是一种特定类型的卷，代表当快照创建时卷上的所有数据。当我们备份进行时，不用担心数据被更改，同时也不需要离线数据系统。

快照卷可以大或者小，但是必须足够容纳快照生命周期中所有有的针对原始卷的改变。

原始卷

root@king:/# lvdisplay /dev/my_volume_group/kinglv   --- Logical volume ---  LV Path                /dev/my_volume_group/kinglv  LV Name                kinglv  VG Name                my_volume_group  LV UUID                lAT5Te-obE1-Q3dY-pU4r-YYDt-rSRu-hgmKQP  LV Write Access        read/write  LV Creation host, time king, 2014-07-27 14:43:41 +0800  LV snapshot status     source of                         dbbackup [active]                         dbbackup2 [active]  LV Status              available  # open                 1  LV Size                100.00 MiB  Current LE             25  Segments               1  Allocation             inherit  Read ahead sectors     auto  - currently set to     256  Block device           252:0

root@king:/# lvcreate -L150 -s -n dbbackup /dev/my_volume_group/kinglv   Rounding up size to full physical extent 152.00 MiB  Logical volume "dbbackup" created

创建一个小于原始的快照卷

root@king:/# lvcreate -L40 -s -n dbbackup2 /dev/my_volume_group/kinglv     Logical volume "dbbackup2" created

创建的两个快照卷

--- Logical volume ---  LV Path                /dev/my_volume_group/dbbackup  LV Name                dbbackup  VG Name                my_volume_group  LV UUID                oj21n8-0h3J-jhI6-e3xm-2zqK-xgTU-1bAf67  LV Write Access        read/write  LV Creation host, time king, 2014-07-27 22:52:35 +0800  LV snapshot status     active destination for kinglv  LV Status              available  # open                 0  LV Size                100.00 MiB  Current LE             25  COW-table size         152.00 MiB  COW-table LE           38  Allocated to snapshot  0.01%  Snapshot chunk size    4.00 KiB  Segments               1  Allocation             inherit  Read ahead sectors     auto  - currently set to     256  Block device           252:1     --- Logical volume ---  LV Path                /dev/my_volume_group/dbbackup2  LV Name                dbbackup2  VG Name                my_volume_group  LV UUID                P1IwY2-Rhyi-CwPU-Hmpw-Qk8c-rKXO-o49wgu  LV Write Access        read/write  LV Creation host, time king, 2014-07-27 22:55:04 +0800  LV snapshot status     active destination for kinglv  LV Status              available  # open                 0  LV Size                100.00 MiB  Current LE             25  COW-table size         40.00 MiB  COW-table LE           10  Allocated to snapshot  0.03%  Snapshot chunk size    4.00 KiB  Segments               1  Allocation             inherit  Read ahead sectors     auto  - currently set to     256  Block device           252:4

卷大小等同于原始卷，但是COW表大小是指定的，当快照满是将被丢弃。

挂载快照卷

root@king:/# mount /dev/my_volume_group/dbbackup /dbbackup/root@king:/# df -hFilesystem                            Size  Used Avail Use% Mounted on/dev/sda1                             5.8G  963M  4.6G  18% /none                                  4.0K     0  4.0K   0% /sys/fs/cgroupudev                                  492M  4.0K  492M   1% /devtmpfs                                 101M  428K  100M   1% /runnone                                  5.0M     0  5.0M   0% /run/locknone                                  501M     0  501M   0% /run/shmnone                                  100M     0  100M   0% /run/user/dev/mapper/my_volume_group-kinglv     93M  1.6M   85M   2% /mnt/dev/mapper/my_volume_group-dbbackup   93M  1.6M   85M   2% /dbbackup

移除快照，先卸载文件系统。

root@king:/# umount /dev/my_volume_group/dbbackuproot@king:/# lvremove /dev/my_volume_group/dbbackupDo you really want to remove and DISCARD active logical volume dbbackup? [y/n]: y  Logical volume "dbbackup" successfully removed