2026-03-12 21:01:38

tiddlywiki/LVM snapshots.txt

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+-- setup 
+pvcreate /dev/xvdc1
+pvcreate /dev/xvdd1
+
+pvs
+  PV         VG Fmt  Attr PSize    PFree
+  /dev/xvdc1    lvm2 ---  <100.00g <100.00g
+  /dev/xvdd1    lvm2 ---  <100.00g <100.00g
+
+vgcreate vg_data /dev/xvdc1 /dev/xvdd1
+
+vgs
+  VG      #PV #LV #SN Attr   VSize   VFree
+  vg_data   2   0   0 wz--n- 199.99g 199.99g
+
+
+lvcreate -n lv_data -L 99G vg_data
+
+mkfs.xfs /dev/vg_data/lv_data
+
+mkdir /mnt/{original,snap}
+
+mount /dev/vg_data/lv_data /mnt/original
+echo "/dev/vg_data/lv_data    /mnt/original    xfs     defaults        0 0" >> /etc/fstab
+
+-- snapshot creation
+lvcreate -L 99G  -s /dev/vg_data/lv_data -n lv_snapshot
+
+-- mount the snapshot LV (on XFS you should use -o nouuid option)
+mount -o nouuid /dev/vg_data/lv_snapshot /mnt/snap/
+
+-- emptying file on snapshot FS
+> /mnt/snap/file_90G.raw
+
+df -h /mnt/snap
+Filesystem                       Size  Used Avail Use% Mounted on
+/dev/mapper/vg_data-lv_snapshot   99G   33M   99G   1% /mnt/snap
+
+-- changes on snaphot FS does not affects data Data% usage on the snaphot LV
+lvs
+  LV          VG      Attr       LSize  Pool Origin  Data%  Meta%  Move Log Cpy%Sync Convert
+  lv_data     vg_data owi-aos--- 99.00g
+  lv_snapshot vg_data swi-aos--- 99.00g      lv_data 0.00
+
+-- change 10Gb of data on source LV
+dd if=/dev/zero of=/mnt/original/file_90G.raw bs=1G count=10
+
+lvdisplay /dev/vg_data/lv_snapshot  | grep "Allocated to snapshot"
+  Allocated to snapshot  10.14%
+
+-- revert to a snapshot
+umount /mnt/{original,snap}
+
+lvconvert --merge /dev/vg_data/lv_snapshot
+
+-- if the COW space is exhausted, LV snapshot status become INACTIVE
+-- we cannot revert from an INACTIVE snapshot
+
+lvdisplay /dev/vg_data/lv_snapshot | grep "LV snapshot status"
+  LV snapshot status     INACTIVE destination for lv_data
+
+lvconvert --merge /dev/vg_data/lv_snapshot
+  Unable to merge invalidated snapshot LV "lv_snapshot".
+
+-- remove a snapshot
+lvremove /dev/vg_data/lv_snapshot
+