LVM还具备有“快照劵”功能，该功能类似于虚拟机软件的还原时间点功能。例如，可以对某一个逻辑卷设备做一次快照，如果日后发现数据被改错了，就可以
利用之前做好的快照劵进行覆盖还原。LVM的快照劵功能有两个特点：
快照劵的容量必须等同于逻辑卷的容量。
快照劵仅一次有效，一旦执行还原操作后则会被立即自动删除。（linux就该这么学p150）
1、首先查看卷组信息
[root@linuxprobe dev]# vgdisplay ## 卷组中已经使用了100MB的容量，空闲容量还有39.89G
--- Volume group ---
VG Name vgtest1
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 4
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 2
Act PV 2
VG Size 39.99 GiB
PE Size 4.00 MiB
Total PE 10238
Alloc PE / Size 25 / 100.00 MiB
Free PE / Size 10213 / 39.89 GiB
VG UUID iPlgk3-b3h6-K3XB-X4vS-ep0B-TL5x-CpjClo
………………
2、向逻辑卷挂载点的目录中写入一个文件
[root@linuxprobe dev]# ls /linuxprobe/
lost+found
[root@linuxprobe dev]# echo "welcome to linuxprobe" > /linuxprobe/readme.txt
[root@linuxprobe dev]# ls /linuxprobe/
lost+found readme.txt
3、使用-s参数生成一个快照劵
[root@linuxprobe dev]# lvcreate -L 100M -s -n SNAPTEST /dev/vgtest1/lvtest1 ## -L 指定快照大小，-n制动快照名称
Logical volume "SNAPTEST" created
[root@linuxprobe dev]# lvdisplay ## 显示详细信息
……………………
--- Logical volume ---
LV Path /dev/vgtest1/SNAPTEST
LV Name SNAPTEST
VG Name vgtest1
LV UUID yfjyWC-uAbi-NBxh-fqCA-XiXq-9Paf-mvzofR
LV Write Access read/write
LV Creation host, time linuxprobe.com, 2020-10-29 17:47:49 +0800
LV snapshot status active destination for lvtest1
LV Status available
# open 0
LV Size 100.00 MiB
Current LE 25
COW-table size 100.00 MiB
COW-table LE 25
Allocated to snapshot 0.01%
Snapshot chunk size 4.00 KiB
Segments 1
Allocation inherit
………………………………
4、在逻辑卷所挂载的目录中创建一个50MB的垃圾文件，然后在查看快照劵的状态。可以发现存储空间占用量上升了？？。
[root@linuxprobe dev]# dd if=/dev/zero bs=50M count=1 of=/linuxprobe/rubbish.txt ## 创建垃圾文件
1+0 records in
1+0 records out
52428800 bytes (52 MB) copied, 1.44275 s, 36.3 MB/s
[root@linuxprobe dev]# lvdisplay ## 查看详细信息
………………
--- Logical volume ---
LV Path /dev/vgtest1/SNAPTEST
LV Name SNAPTEST
VG Name vgtest1
LV UUID yfjyWC-uAbi-NBxh-fqCA-XiXq-9Paf-mvzofR
LV Write Access read/write
LV Creation host, time linuxprobe.com, 2020-10-29 17:47:49 +0800
LV snapshot status active destination for lvtest1
LV Status available
# open 0
LV Size 100.00 MiB
Current LE 25
COW-table size 100.00 MiB
COW-table LE 25
Allocated to snapshot 45.32%
Snapshot chunk size 4.00 KiB
Segments 1
Allocation inherit
Read ahead sectors auto
……………………
5、先卸载逻辑卷设备的挂载
[root@linuxprobe dev]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 18G 2.9G 15G 17% /
devtmpfs 985M 0 985M 0% /dev
tmpfs 994M 80K 994M 1% /dev/shm
tmpfs 994M 8.9M 986M 1% /run
tmpfs 994M 0 994M 0% /sys/fs/cgroup
/dev/sda1 497M 119M 379M 24% /boot
/dev/sr0 3.5G 3.5G 0 100% /run/media/root/RHEL-7.0 Server.x86_64
/dev/mapper/vgtest1-lvtest1 93M 52M 35M 61% /linuxprobe
[root@linuxprobe dev]# umount /linuxprobe/ ## 卸载
[root@linuxprobe dev]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 18G 2.9G 15G 17% /
devtmpfs 985M 0 985M 0% /dev
tmpfs 994M 80K 994M 1% /dev/shm
tmpfs 994M 8.9M 986M 1% /run
tmpfs 994M 0 994M 0% /sys/fs/cgroup
/dev/sda1 497M 119M 379M 24% /boot
/dev/sr0 3.5G 3.5G 0 100% /run/media/root/RHEL-7.0 Server.x86_64
6、为了校验SNAPTEST快照劵的效果，需要对逻辑卷进行快照还原操作。
[root@linuxprobe dev]# lvconvert --merge /dev/vgtest1/SNAPTEST ## 还原
Merging of volume SNAPTEST started.
lvtest1: Merged: 65.9%
lvtest1: Merged: 100.0%
Merge of snapshot into logical volume lvtest1 has finished.
Logical volume "SNAPTEST" successfully removed
6、快照被自动删除了，rubbish.txt也被删除了
[root@linuxprobe dev]# mount -a ## 挂载
[root@linuxprobe dev]# ls /dev/vgtest1/
lvtest1
[root@linuxprobe dev]# ls /linuxprobe/
lost+found readme.txt