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Linux: LVM thin volume and snapshot

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LVM: logical volume manager

Advantage: give more flexible of space

LVM thin volume

Create thin pool first

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[root@client ~]# lvcreate -L 1G -T thin_vg/thinpool
  Using default stripesize 64.00 KiB.
  Logical volume "thinpool" created.
[root@client ~]# lvdisplay thin_vg/thinpool
  --- Logical volume ---
  LV Name                thinpool
  VG Name                thin_vg
  LV UUID                ncc3Kh-eZgD-WLQn-F4cq-pPJJ-rYjD-XsTx34
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-12 13:02:42 -0700
  LV Pool metadata       thinpool_tmeta
  LV Pool data           thinpool_tdata
  LV Status              available
  # open                 0
  LV Size                1.00 GiB
  Allocated pool data    0.00%
  Allocated metadata     0.98%
  Current LE             256
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:6

Create a thin1 on thinpool

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[root@client ~]# lvcreate -V 10G -T thin_vg/thinpool -n annathin1
  Using default stripesize 64.00 KiB.
  WARNING: Sum of all thin volume sizes (10.00 GiB) exceeds the size of thin pool thin_vg/thinpool and the size of whole volume group (2.00 GiB)!
  For thin pool auto extension activation/thin_pool_autoextend_threshold should be below 100.
  Logical volume "annathin1" created.
[root@client ~]# lvdisplay thin_vg
  --- Logical volume ---
  LV Name                thinpool
  VG Name                thin_vg
  LV UUID                ncc3Kh-eZgD-WLQn-F4cq-pPJJ-rYjD-XsTx34
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-12 13:02:42 -0700
  LV Pool metadata       thinpool_tmeta
  LV Pool data           thinpool_tdata
  LV Status              available
  # open                 2
  LV Size                1.00 GiB
  Allocated pool data    0.00%
  Allocated metadata     1.07%
  Current LE             256
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:6
   
  --- Logical volume ---
  LV Path                /dev/thin_vg/annathin1
  LV Name                annathin1
  VG Name                thin_vg
  LV UUID                q47tG0-P2xf-CMsw-a2tE-SgWl-gjni-VJD1jA
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-12 13:09:12 -0700
  LV Pool name           thinpool
  LV Status              available
  # open                 0
  LV Size                10.00 GiB
  Mapped size            0.00%
  Current LE             2560
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:8
[root@client /]# mkfs.xfs /dev/thin_vg/annathin1 
meta-data=/dev/thin_vg/annathin1 isize=512    agcount=16, agsize=163824 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=2621184, imaxpct=25
         =                       sunit=16     swidth=16 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@client /]# mkdir /mnt/annathin1
[root@client /]# mount /dev/thin_vg/annathin1 /mnt/annathin1/
[root@client /]# df -Th /mnt/annathin1
Filesystem                    Type      Size  Used Avail Use% Mounted on
/dev/mapper/thin_vg-annathin1 xfs        10G   33M   10G   1% /mnt/annathin1

copy some files to annathin1

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[root@client ]# cp -a /etc/vsftpd/ /mnt/annathin1/
[root@client ]# cp -a /usr/share/doc/man-db-2.6.3/  /mnt/annathin1/
[root@client annathin1]# ll
total 0
drwxr-xr-x. 2 root root 113 Jun  2  2017 man-db-2.6.3
drwxr-xr-x. 2 root root 128 Apr  4 12:46 vsftpd
[root@client ~]# df -Th /mnt/annathin1/
Filesystem                    Type  Size  Used Avail Use% Mounted on
/dev/mapper/thin_vg-annathin1 xfs    10G   34M   10G   1% /mnt/annathin1

The vg thin_vg actually only has 1G, but it shows 10G after create thinpool. That is the magical of LVM thinpool.
Note: users are not supposed to exceed actual 1G volume even though it shows having 10G volume, otherwise it will destory the filesystem!

LVM snapshot

create a snapshot for annathin1

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[root@client ~]# lvcreate -s -l 99 -n  thinpool_snapshot  /dev/thin_vg/annathin1
  Using default stripesize 64.00 KiB.
  WARNING: Sum of all thin volume sizes (10.00 GiB) exceeds the size of thin pools and the size of whole volume group (2.00 GiB)!
  For thin pool auto extension activation/thin_pool_autoextend_threshold should be below 100.
  Logical volume "thinpool_snapshot" created.
[root@client ~]# lvdisplay /dev/thin_vg/thinpool_snapshot 
  --- Logical volume ---
  LV Path                /dev/thin_vg/thinpool_snapshot
  LV Name                thinpool_snapshot
  VG Name                thin_vg
  LV UUID                4fYojx-SvHi-5IVX-aoIk-RxpD-8Nlb-1hHK3g
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-14 17:01:32 -0700
  LV snapshot status     active destination for annathin1
  LV Status              available
  # open                 0
  LV Size                10.00 GiB
  Current LE             2560
  COW-table size         396.00 MiB
  COW-table LE           99
  Allocated to snapshot  0.02%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:11


[root@client ~]# lvdisplay /dev/thin_vg/annathin1 
  --- Logical volume ---
  LV Path                /dev/thin_vg/annathin1
  LV Name                annathin1
  VG Name                thin_vg
  LV UUID                q47tG0-P2xf-CMsw-a2tE-SgWl-gjni-VJD1jA
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-12 13:09:12 -0700
  LV snapshot status     source of
                         thinpool_snapshot [active]
  LV Pool name           thinpool
  LV Status              available
  # open                 1
  LV Size                10.00 GiB
  Mapped size            0.12%
  Current LE             2560
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:8

Mount

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[root@client /]# mkdir  /mnt/snapshot
[root@client snapshot]# blkid
/dev/mapper/thin_vg-annathin1: UUID="93b48865-b28d-4e2e-b76e-893e804d944c" TYPE="xfs" 
/dev/mapper/thin_vg-thinpool_snapshot: UUID="93b48865-b28d-4e2e-b76e-893e804d944c" TYPE="xfs"
[root@client /]# mount -o nouuid /dev/thin_vg/thinpool_snapshot  /mnt/snapshot
[root@client /]# df -Th
Filesystem                            Type      Size  Used Avail Use% Mounted on
/dev/mapper/thin_vg-annathin1         xfs        10G   34M   10G   1% /mnt/annathin1
/dev/mapper/thin_vg-thinpool_snapshot xfs        10G   34M   10G   1% /mnt/snapshot

Due to snapshot, /dev/thin_vg/annathin1 and /dev/thin_vg/thinpool_snapshot have same uuid. When mount to mount point, users need to use “nouuid” arguments.

make some changes on the /mnt/annathin1 dir

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[root@client man-db-2.6.3]# rm ChangeLog
rm: remove regular file ‘ChangeLog’?
[root@client man-db-2.6.3]# df -Th /mnt/annathin1/ /mnt/snapshot/
Filesystem                            Type  Size  Used Avail Use% Mounted on
/dev/mapper/thin_vg-annathin1         xfs    10G   33M   10G   1% /mnt/annathin1
/dev/mapper/thin_vg-thinpool_snapshot xfs    10G   34M   10G   1% /mnt/snapshot

check the status of snapshot after doing the change on the original annathin1 dir

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[root@client man-db-2.6.3]# lvdisplay /dev/thin_vg/thinpool_snapshot 
  --- Logical volume ---
  LV Path                /dev/thin_vg/thinpool_snapshot
  LV Name                thinpool_snapshot
  VG Name                thin_vg
  LV UUID                eT1j03-4v5E-7fUi-BSV0-6dun-RCL1-fy9atx
  LV Write Access        read/write
  LV Creation host, time client.centos7.study, 2019-07-14 17:18:16 -0700
  LV snapshot status     active destination for annathin1
  LV Status              available
  # open                 1
  LV Size                10.00 GiB
  Current LE             2560
  COW-table size         396.00 MiB
  COW-table LE           99
  Allocated to snapshot  0.52%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:11

It shows the snapshot has been used 0.52%

next, we will restore annathin1 by snapshot, we will backup snapshot first.

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[root@client ~]# xfsdump -l 0 -L lvm1 -M lvm1 -f /tmp/backup.lvm    /mnt/snapshot
xfsdump: using file dump (drive_simple) strategy
xfsdump: version 3.1.4 (dump format 3.0) - type ^C for status and control
xfsdump: level 0 dump of client.centos7.study:/mnt/snapshot
xfsdump: dump date: Sun Jul 14 17:31:38 2019
xfsdump: session id: 5ea4e354-bf53-4069-8b63-ec4c2259c444
xfsdump: session label: "lvm1"
xfsdump: ino map phase 1: constructing initial dump list
xfsdump: ino map phase 2: skipping (no pruning necessary)
xfsdump: ino map phase 3: skipping (only one dump stream)
xfsdump: ino map construction complete
xfsdump: estimated dump size: 786816 bytes
xfsdump: creating dump session media file 0 (media 0, file 0)
xfsdump: dumping ino map
xfsdump: dumping directories
xfsdump: dumping non-directory files
xfsdump: ending media file
xfsdump: media file size 775272 bytes
xfsdump: dump size (non-dir files) : 745816 bytes
xfsdump: dump complete: 1 seconds elapsed
xfsdump: Dump Summary:
xfsdump:   stream 0 /tmp/backup.lvm OK (success)
xfsdump: Dump Status: SUCCESS
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[root@client ~]# umount /mnt/snapshot
[root@client ~]# lvremove /dev/thin_vg/thinpool_snapshot 
Do you really want to remove active logical volume thin_vg/thinpool_snapshot? [y/n]: y
  Logical volume "thinpool_snapshot" successfully removed
[root@client ~]# umount /mnt/annathin1/
[root@client ~]# mkfs.xfs -f /dev/thin_vg/annathin1 
meta-data=/dev/thin_vg/annathin1 isize=512    agcount=16, agsize=163824 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=2621184, imaxpct=25
         =                       sunit=16     swidth=16 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@client ~]# mount /dev/thin_vg/annathin1  /mnt/annathin1/

[root@client ~]# xfsrestore -f /tmp/backup.lvm -L lvm1 /mnt/annathin1/
xfsrestore: using file dump (drive_simple) strategy
xfsrestore: version 3.1.4 (dump format 3.0) - type ^C for status and control
xfsrestore: searching media for dump
xfsrestore: examining media file 0
xfsrestore: found dump matching specified label:
xfsrestore: hostname: client.centos7.study
xfsrestore: mount point: /mnt/snapshot
xfsrestore: volume: /dev/mapper/thin_vg-thinpool_snapshot
xfsrestore: session time: Sun Jul 14 17:31:38 2019
xfsrestore: level: 0
xfsrestore: session label: "lvm1"
xfsrestore: media label: "lvm1"
xfsrestore: file system id: 93b48865-b28d-4e2e-b76e-893e804d944c
xfsrestore: session id: 5ea4e354-bf53-4069-8b63-ec4c2259c444
xfsrestore: media id: e223f10b-7718-4801-bda7-7e066e59deb1
xfsrestore: using online session inventory
xfsrestore: searching media for directory dump
xfsrestore: reading directories
xfsrestore: 3 directories and 13 entries processed
xfsrestore: directory post-processing
xfsrestore: restoring non-directory files
xfsrestore: restore complete: 0 seconds elapsed
xfsrestore: Restore Summary:
xfsrestore:   stream 0 /tmp/backup.lvm OK (success)
xfsrestore: Restore Status: SUCCESS

[root@client ~]# df -Th  /mnt/annathin1/
Filesystem                    Type  Size  Used Avail Use% Mounted on
/dev/mapper/thin_vg-annathin1 xfs    10G   34M   10G   1% /mnt/annathin1

It shows the annathins dir back from 33M to 34M, the original one.