First the situation without the snapshoted logical volume:
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[root@lxctest ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_system-lv--root 9.8G 1.2G 8.2G 12% /
devtmpfs 7.8G 0 7.8G 0% /dev
tmpfs 7.8G 0 7.8G 0% /dev/shm
tmpfs 7.8G 8.7M 7.8G 1% /run
tmpfs 7.8G 0 7.8G 0% /sys/fs/cgroup
/dev/mapper/centos_backup-lv--backup_vm 466G 17M 464G 1% /backup/vm
/dev/mapper/centos_backup-lv--backup_host 466G 160M 464G 1% /backup/host
/dev/md0 991M 112M 828M 12% /boot
/dev/mapper/centos_system-lv--var 3.9G 619M 3.0G 17% /var
/dev/mapper/centos_system-lv--var_log 7.8G 41M 7.3G 1% /var/log
/dev/mapper/centos_system-lv--tmp 3.9G 17M 3.6G 1% /tmp
tmpfs 1.6G 0 1.6G 0% /run/user/0
/dev/mapper/lxc_crypt 154G 426M 152G 1% /var/lib/lxc
/dev/mapper/centos_data-lv--virtdata 154G 17M 152G 1% /var/lib/libvirt
[root@lxctest ~]# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,size=8103848k,nr_inodes=2025962,mode=755)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids)
cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_prio,net_cls)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct,cpu)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mapper/centos_system-lv--root on / type ext4 (rw,relatime,data=ordered)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=31,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=12673)
mqueue on /dev/mqueue type mqueue (rw,relatime)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
/dev/mapper/centos_backup-lv--backup_vm on /backup/vm type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/mapper/centos_backup-lv--backup_host on /backup/host type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/md0 on /boot type ext3 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--var on /var type ext4 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--var_log on /var/log type ext4 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--tmp on /tmp type ext4 (rw,relatime,data=ordered)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw,relatime)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,size=1622936k,mode=700)
/dev/mapper/lxc_crypt on /var/lib/lxc type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/mapper/centos_data-lv--virtdata on /var/lib/libvirt type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
Now I will create a Snapshot of /dev/centos_data/lv-virtdata:
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[root@lxctest ~]# lvcreate --snapshot --extents 100%FREE --name some_snap /dev/centos_data/lv-virtdata
Using default stripesize 64.00 KiB.
Logical volume "some_snap" created.
[root@lxctest ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_system-lv--root 9.8G 1.2G 8.2G 12% /
devtmpfs 7.8G 0 7.8G 0% /dev
tmpfs 7.8G 0 7.8G 0% /dev/shm
tmpfs 7.8G 8.7M 7.8G 1% /run
tmpfs 7.8G 0 7.8G 0% /sys/fs/cgroup
/dev/mapper/centos_backup-lv--backup_vm 466G 17M 464G 1% /backup/vm
/dev/mapper/centos_backup-lv--backup_host 466G 160M 464G 1% /backup/host
/dev/md0 991M 112M 828M 12% /boot
/dev/mapper/centos_system-lv--var 3.9G 619M 3.0G 17% /var
/dev/mapper/centos_system-lv--var_log 7.8G 41M 7.3G 1% /var/log
/dev/mapper/centos_system-lv--tmp 3.9G 17M 3.6G 1% /tmp
tmpfs 1.6G 0 1.6G 0% /run/user/0
/dev/mapper/lxc_crypt 154G 426M 152G 1% /var/lib/lxc
/dev/mapper/centos_data-some_snap 154G 17M 152G 1% /var/lib/libvirt
[root@lxctest ~]# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,size=8103848k,nr_inodes=2025962,mode=755)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids)
cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_prio,net_cls)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct,cpu)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mapper/centos_system-lv--root on / type ext4 (rw,relatime,data=ordered)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=31,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=12673)
mqueue on /dev/mqueue type mqueue (rw,relatime)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
/dev/mapper/centos_backup-lv--backup_vm on /backup/vm type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/mapper/centos_backup-lv--backup_host on /backup/host type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/md0 on /boot type ext3 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--var on /var type ext4 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--var_log on /var/log type ext4 (rw,relatime,data=ordered)
/dev/mapper/centos_system-lv--tmp on /tmp type ext4 (rw,relatime,data=ordered)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw,relatime)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,size=1622936k,mode=700)
/dev/mapper/lxc_crypt on /var/lib/lxc type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
/dev/mapper/centos_data-some_snap on /var/lib/libvirt type btrfs (rw,relatime,nodatasum,nodatacow,space_cache,subvolid=5,subvol=/)
So you see, prior is the normal situation with the mountpoints mounted according to /etc/fstab. After executing the snapshot command, the newly created logical volume, containing the
snapshot of the original logical volume is mounted in place of the original logical volume.
Here is my fstab:
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[root@lxctest ~]# cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Fri Sep 7 10:59:38 2018
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/centos_system-lv--root / ext4 defaults 1 1
/dev/mapper/centos_backup-lv--backup_host /backup/host btrfs defaults,nodatacow 1 2
/dev/mapper/centos_backup-lv--backup_vm /backup/vm btrfs defaults,nodatacow 1 2
UUID=a4139cce-75b9-46b4-aa8c-62496d2dcaad /boot ext3 defaults 1 2
/dev/mapper/centos_system-lv--tmp /tmp ext4 defaults 1 2
/dev/mapper/centos_system-lv--var /var ext4 defaults 1 2
/dev/mapper/centos_data-lv--virtdata /var/lib/libvirt btrfs defaults,nodatacow 1 2
/dev/mapper/lxc_crypt /var/lib/lxc btrfs defaults,nodatacow 1 2
#/dev/mapper/centos_data-lv--lxcdata /var/lib/lxc btrfs defaults,nodatacow 1 2
/dev/mapper/centos_system-lv--var_log /var/log ext4 defaults 1 2
/dev/mapper/centos_system-lv--swap swap swap defaults 0 0
And thank you both for taking the time to analyze my problem.