测试LVM的快照功能

　　三 测试给lv01建立快照
　　1、创建快照
　　[root@tvm-test /]# lvcreate -L 2G -s -n snap_lv01  /dev/vg01/lv01
　　Logical volume "snap_lv01" created
　　2、挂载后压缩备份
　　[root@tvm-test ~]# lv_snap="/dev/vg01/snap_lv01"
　　&& d_backup='/data/backup/snapshot'
　　&& f_snap="/data/backup/snapshot/lv01_$(date +%F).tar.gz"
　　test -d ${d_backup} || mkdir -p ${d_backup}/mnt
　　&& mount -o ro ${lv_snap} ${d_backup}/mnt
　　&& cd ${d_backup}
　　&& tar zcf ${f_snap} mnt/*
　　&& ls -lh ${f_snap}
　　&& df -h
　　-rw-r--r-- 1 root root 438K Jul 31 16:23 /data/backup/snapshot/lv01_2015-07-31.tar.gz
　　Filesystem                  Size  Used Avail Use% Mounted on
　　/dev/sda3                   3.8G  1.7G  2.0G  46% /
　　tmpfs                       246M   12K  246M   1% /dev/shm
　　/dev/sda1                   194M   29M  155M  16% /boot
　　/dev/mapper/vg01-lv01       9.9G  590M  8.8G   7% /DATA01
　　/dev/mapper/vg01-snap_lv01  9.9G  590M  8.8G   7% /data/backup/snapshot/mnt
　　3、卸载后移除快照
　　[root@tvm-test /]# umount ${d_backup}/mnt && lvremove -f ${lv_snap}
　　Logical volume "snap_lv01" successfully removed
　　4、总结步骤
#1 create 创建快照
#2 mount to tar backup 挂载后压缩备份
#3 umount to remove 卸载后移除快照
（可以写成脚本了）
[root@tvm-test bin]# cat lvm_test_snapshot.sh
#!/bin/bash
#
# 2015/7/31
n_size='2G'
f_vg='vg01'
f_orin='lv01'
f_snap='snap_lv01'
lv_orig="/dev/${f_vg}/${f_orig}"
lv_snap="/dev/${f_vg}/${f_snap}"
d_backup='/data/backup/snapshot'
f_snap="${d_backup}/${f_orig}_$(date +%F).tar.gz"
#1 create 创建快照
lvcreate -L ${n_size} -s -n ${f_snap} ${lv_orig}
#2 mount to tar backup 挂载后压缩备份
test -d ${d_backup} || mkdir -p ${d_backup}/mnt
&& mount -o remount，ro ${lv_snap} ${d_backup}/mnt
&& df -h
cd ${d_backup}
&& tar zcf ${f_snap} mnt/*
&& ls -lh ${f_snap}
#3 umount to remove 卸载后移除快照
umount ${d_backup}/mnt && lvremove -f ${lv_snap}
　　四、疑问
　　Q：建立快照时，要分配多大的size呢？
　　A：翻一下lvcreate的man，注意-s选项的描述中有这么一段话：
　　The non thin volume snapshot with the specified size does  not need  the
　　same  amount  of  storage  the origin has. In a typical scenario， 15-20%
　　might be enough. In case the snapshot runs out of storage， use  lvextend(8)
　　to  grow  it.  Shrinking  a snapshot is supported by lvreduce(8) as well.
　　Run lvs(8) on the snapshot in order to check how much  data  is  allocated
　　to it.  Note: a small amount of the space you allocate to the snapshot is
　　used to track the locations of the chunks of data， so you should allocate
　　slightly  more space than you actually need and monitor (--monitor) the rate
　　at which the snapshot data is growing so you can avoid running out of space.
　　给snapshot分配20%左右的origin的容量即可。
　　测试：
[root@tvm-test /]# dd if=/dev/zero of=/DATA01/dir2_3/test3.dd bs=4096 count=200000
200000+0 records in
200000+0 records out
819200000 bytes (819 MB) copied， 1.21615 s， 674 MB/s
[root@tvm-test snapshot]# rm -f /DATA01/dir2_3/test2.dd
[root@tvm-test snapshot]# pwd
/data/backup/snapshot
[root@tvm-test snapshot]# ls
lv01_2015-07-31.tar.gz  mnt
[root@tvm-test snapshot]# tar zxvf lv01_2015-07-31.tar.gz
mnt/dir2_1/
mnt/dir2_1/file3.aa
mnt/dir2_1/file3.bb
mnt/dir2_1/file3.cc
mnt/dir2_2/
mnt/dir2_2/file3.aa
mnt/dir2_2/file3.bb
mnt/dir2_2/file3.cc
mnt/dir2_3/
mnt/dir2_3/test2.dd
mnt/dir2_3/test1.dd
mnt/file2_1
mnt/file2_2
mnt/file2_3
mnt/file2_4
mnt/file2_5
[root@tvm-test snapshot]# ls mnt/
dir2_1  dir2_2  dir2_3  file2_1  file2_2  file2_3  file2_4  file2_5
[root@tvm-test snapshot]# ll -h mnt/dir2_3/
total 440M
-rw-r--r-- 1 root root  49M Jul 31 15:35 test1.dd
-rw-r--r-- 1 root root 391M Jul 31 15:36 test2.dd
　　拷贝到另一台主机：
　　[root@tvm-test snapshot]# rsync -avzP lv01_2015-07-31.tar.gz 192.168.56.253:/data/testarea
　　The authenticity of host '192.168.56.253 (192.168.56.253)' can't be established.
　　RSA key fingerprint is 35:10:6d:25:4e:3d:6f:59:86:87:e3:88:9f:9c:81:a8.
　　Are you sure you want to continue connecting (yes/no)? yes
　　Warning: Permanently added '192.168.56.253' (RSA) to the list of known hosts.
　　root@192.168.56.253's password:
　　sending incremental file list
　　lv01_2015-07-31.tar.gz
　　447649    79.13MB/s    0:00:00 (xfer#1， to-check=0/1)
　　sent 447890 bytes  received 31 bytes  68910.92 bytes/sec
　　total size is 447649  speedup is 1.00
　　在另一台主机上操作：
[root@tvm-saltmaster testarea]# ll -h
total 440K
-rw-r--r-- 1 root root 438K Jul 31 16:23 lv01_2015-07-31.tar.gz
[root@tvm-saltmaster testarea]# tar zxvf lv01_2015-07-31.tar.gz
mnt/dir2_1/
mnt/dir2_1/file3.aa
mnt/dir2_1/file3.bb
mnt/dir2_1/file3.cc
mnt/dir2_2/
mnt/dir2_2/file3.aa
mnt/dir2_2/file3.bb
mnt/dir2_2/file3.cc
mnt/dir2_3/
mnt/dir2_3/test2.dd
mnt/dir2_3/test1.dd
mnt/file2_1
mnt/file2_2
mnt/file2_3
mnt/file2_4
mnt/file2_5
[root@tvm-saltmaster testarea]# ls mnt/
dir2_1  dir2_2  dir2_3  file2_1  file2_2  file2_3  file2_4  file2_5
[root@tvm-saltmaster testarea]# ll -h mnt/dir2_3/
total 440M
-rw-r--r-- 1 root root  49M Jul 31 15:35 test1.dd
-rw-r--r-- 1 root root 391M Jul 31 15:36 test2.dd