1、邏輯卷管理器快照

1、快照是特殊的邏輯卷，它是在生成快照時存在的邏輯卷的準確拷貝

2、對於需要備份或者複製的現有資料臨時拷貝以及其它操作來說，快照是最合適的選擇

3、建立的前提，快照和邏輯卷在同一個卷組中， 在生成快照時會分配給它一定的空間，快照中的資料是邏輯卷的原始資料，一旦邏輯卷中的資料發生變動，立即會被複制至快照中，當邏輯卷的快照還原後，快照的生命週期結束；建立快照的卷大小小於等於原始邏輯卷,也可以使用lvextend擴充套件快照

4、快照就是將當時的系統資訊記錄下來，就好像照相一般，若將來有任何資料改動了，則原始資料會被移動到快照區，沒有改動的區域則由快照區和檔案系統共享

5、由於快照區與原本的LV共用很多PE的區塊，因此快照與被快照的LV必須在同一個VG中.系統恢復的時候的檔案數量不能高於快照區的實際容量

2、為現有邏輯卷建立照

1、現有的邏輯卷
[root@centos_8 ~]# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/vg1/xzcdc
  LV Name                xzcdc
  VG Name                vg1
  LV UUID                8FTXa6-PWyC-RN9Q-3kXu-cEmf-oxfT-kwk9yk
  LV Write Access        read/write
  LV Creation host, time centos_8, 2021-12-15 19:26:40 +0800
  LV Status              available
  # open                 0
  LV Size                10.00 GiB
  Current LE             2560
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:0
2、建立快照
[root@centos_8 ~]# lvcreate -L +3G -s -n data-snapshot -p  /dev/vg1/xzcdc
[root@centos_8 ~]# lvs
  LV            VG  Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  data-snapshot vg1 sri-a-s---  3.00g      xzcdc  0.00                                   
  xzcdc         vg1 owi-a-s--- 10.00g  
  
  [root@centos_8 ~]# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/vg1/xzcdc
  LV Name                xzcdc
  VG Name                vg1
  LV UUID                8FTXa6-PWyC-RN9Q-3kXu-cEmf-oxfT-kwk9yk
  LV Write Access        read/write
  LV Creation host, time centos_8, 2021-12-15 19:26:40 +0800
  LV snapshot status     source of
                         data-snapshot [active]
  LV Status              available
  # open                 0
  LV Size                10.00 GiB
  Current LE             2560
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:0
   
  --- Logical volume ---
  LV Path                /dev/vg1/data-snapshot
  LV Name                data-snapshot
  VG Name                vg1
  LV UUID                9RZuZq-7tDr-LDVx-1QA7-jdd1-33De-yk2eP1
  LV Write Access        read only
  LV Creation host, time centos_8, 2021-12-15 19:30:51 +0800
  LV snapshot status     active destination for xzcdc
  LV Status              available
  # open                 0
  LV Size                10.00 GiB
  Current LE             2560
  COW-table size         3.00 GiB
  COW-table LE           768
  Allocated to snapshot  0.00%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:3
   
3、掛載快照
[root@centos_8 ~]#  mkdir -p /mnt/snap
[root@centos_8 ~]#  mount -o ro /dev/vg1/data-snapshot /mnt/snap
 

3、LVM xfs快照

1、完成邏輯卷
[root@centos_8 ~]# pvcreate /dev/sdc
  Physical volume "/dev/sdc" successfully created.

[root@centos_8 ~]# vgcreate vg0 /dev/sdc
Volume group "vg0" successfully created

[root@centos_8 ~]# lvcreate -n mysql -L +19G  vg0
Logical volume "mysql" created.
2、建立xfs快照
[root@centos_8 ~]# lvcreate  -n mysql-back -s -L 10M /dev/vg0/mysql
  Rounding up size to full physical extent 12.00 MiB
  Logical volume "mysql-back" created.
--- Logical volume ---
  LV Path                /dev/vg0/mysql-back
  LV Name                mysql-back
  VG Name                vg0
  LV UUID                uR9wV8-ylWj-Qpvm-ne8L-U9Tv-yDia-xo5bbk
  LV Write Access        read/write
  LV Creation host, time centos_8, 2021-12-15 19:44:36 +0800
  LV snapshot status     active destination for mysql
  LV Status              available
  # open                 0
  LV Size                19.00 GiB
  Current LE             4864
  COW-table size         12.00 MiB
  COW-table LE           3
  Allocated to snapshot  0.00%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:7
3、格式化為xfs檔案系統
[root@centos_8 ~]# mkfs.xfs /dev/vg0/mysql
meta-data=/dev/vg0/mysql         isize=512    agcount=4, agsize=1245184 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=4980736, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@centos_8 ~]# mkfs.xfs /dev/vg0/mysql-back 
meta-data=/dev/vg0/mysql-back    isize=512    agcount=4, agsize=1245184 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=4980736, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0


4、在xfs檔案系統中，建立快照的時候，要有讀寫許可權，不然會掛載不了的
[root@centos_8 ~]# mkdir -pv /mnt/{mysql,snap}
[root@centos_8 ~]# mount -o nouuid /dev/vg0/mysql-back /mnt/snap/
[root@centos_8 ~]# df
Filesystem                  1K-blocks    Used Available Use% Mounted on
/dev/sda2                    20961280 3636392  17324888  18% /
devtmpfs                       805608       0    805608   0% /dev
tmpfs                          821536       0    821536   0% /dev/shm
tmpfs                          821536   10476    811060   2% /run
tmpfs                          821536       0    821536   0% /sys/fs/cgroup
/dev/sda3                     5232640   32948   5199692   1% /data
/dev/sda1                    15718400  158004  15560396   2% /boot
tmpfs                          164308      12    164296   1% /run/user/42
tmpfs                          164308       0    164308   0% /run/user/0
/dev/mapper/vg0-mysql--back  19912704   32944  19879760   1% /mnt/snap
/dev/mapper/vg0-mysql        19912704   32944  19879760   1% /mnt/mysql

4、檢視資料是否同步

5、恢復快照
  [root@centos_8 ~]# umount /mnt/sanp/
  [root@centos_8 ~]# umount /mnt/mysql/
  [root@centos_8 ~]# lvconvert --merge /dev/vg0/mysql-back 
  
  6、刪除快照
  umount /mnt/mysql-back 
lvremove /dev/vg0/mysql-back