Hi,
Currently we can convert a standard LV to a thin LV with an
external, read only origin as per man lvmthin. Unwritten portions
of the thin LV are read from the external LV. I assume that new
portions are written to a thin snapshot, but the man page is
silent about this.
lvconvert --type thin --thinpool VG/ThinPoolLV --originname NewExternalOriginLV VG/ExampleLV
This means the external LV is needed forever, even if all of its
extents are outdated and replaced by thin extents. I'd like to get
a full conversion to a ThinLV by modifying only meta data.
Within lvconvert:
0) Use external thin LV as above as the starting point
1) Create new ThinLV stub
2) Assign extents of external LV to thin pool in a 'used', read
only state.
3) Assign extents of external LV to new ThinLV .
4) Switch link of the thin snapshot to the new ThinLV
5) Make ThinLV read only
6) Remove external LV stub
To release the outdated ThinLV extents, we just need to merge the
initial thin snapshot with it.
One great use case is instant bare metal recovery: Create an
empty ThinPool on proper HW and just activate the external volumes
(on USB Disks). Redundancy is then restored in the background by
converting to a Thin LV as above and 'pvmove'ing.
Creating these backups would also need a way to 'unthin' an LV
snapshot to a 'thick' LV with an independent copy of all extents.
Can we already to this by e. g. creating and splitting a mirror?
Or by merging with an empty 'thick' LV? Or do we need the above
steps in the opposite direction?
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