[linux-lvm] unexpected behaviour of "lvresize" with sparse volumes

Zdenek Kabelac zdenek.kabelac at gmail.com
Thu Oct 15 09:24:39 UTC 2015

Dne 15.10.2015 v 09:13 Alexey napsal(a):
> Hello,
> If you look at the output of `lvs myvg`, then you will understand whats happens.
> When you create thin LV without specifying option `-T`, lvm automatically
> created TP for you with size equal to -L option.
> And when you resize your sparsevol, your TP (auto name lvol1) still have old
> size.

Mixing 2 things together.

Newer lvm2 tools (then reported 2.02.98)  are now creating sparse volumes
as a thin volume in thin-pool.

Old behavior with /dev/zero snapshot is thought still available
either with lvm.conf settings  or using  --type snapshot.

Now back to the  original problem - yep you cannot resize it with tool ATM.

There will be likely added support  for    'lvresize -V+'
(it will work for thin volumes & these sparse snapshot)

Basically adding 'virtual size'.

But it has lower priority ATM (as you may resize thin volumes
with -L, and thus users do not have much troubles with it,
expect the logical meaning looks 'wrong' - as resize of thin
volume does not really 'eat' extents from VG.

If you 'urgently' need  bigger size -

- make sure  modified LVs are rather deactivated.
- 'vgcfgbackup' your vg
- take your favourite text editor (e.g.  vi)
- edit size for your '_vorigin' LV (extent_count = ....)
- edit size for respective hidden 'snapshot0' LV (extent_count = ....)
   (if you have more then one -
    find properly numbered one, the one referencing your _vorigin! -
    those 2 LVs should have equal size)
- 'vgcfgrestore'  your updated metadata
- activate now bigger sized _vorigin
- check  blockdev --getsize64  /dev/vg/sparsevol has new correct size
- enjoy



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