lvmthin on top of lvmvdo - space of removed thin snapshots of thin volumes is not discarded on lvmvdo

[maurerh]

Hi

I am running LVM2 2.03.24.
When I create a thinpool on top of LVM using

lvcreate --type thin-pool -n lv_data_pool -L 350G --pooldatavdo y VolGroupVDO  --chunksize 64k
lvrename VolGroupVDO/lv_data_pool_vpool0 VolGroupVDO/lv_data_vdo_vpool0
lvextend --poolmetadatasize 16G VolGroupVDO/lv_data_pool
lvextend -L+1650G VolGroupVDO/lv_data_pool
lvcreate  --thin VolGroupVDO/lv_data_pool --virtualsize 1T --name lvdata

This leads to the following LVM setup

  lv_data_pool               VolGroupVDO twi-a-t---   1,95t                           0,00   0,15
  [lv_data_pool_tdata]       VolGroupVDO vwi-aov---   1,95t lv_data_vdo_vpool0        0,00
  [lv_data_pool_tmeta]       VolGroupVDO ewi-ao---- <15,88g
  lv_data_vdo_vpool0         VolGroupVDO dwi------- 350,00g                           1,21
  [lv_data_vdo_vpool0_vdata] VolGroupVDO Dwi-ao---- 350,00g
  lvdata                     VolGroupVDO Vwi-a-t---   1,00t lv_data_pool              0,00
  [lvol0_pmspare]            VolGroupVDO ewi------- <15,88g

If I write data to the filesystem and delete it, discards work on vdo layer and space is discared as expected and
vdostats --hu
reduces the usage.
VolGroupVDO-lv_data_vdo_vpool0-vpool 350.0G 4.2G 345.8G 1% 99%

If I write data to the file system, create a thin snapshot with
lvcreate -s --name lvdata_s1 VolGroupVDO/lvdata
delete the data in the original filesystem, the usage of vdo does not change as expected.

But if i delete the snapshot, with
lvremove VolGroupVDO/lvdata_s1
I would expect, that the VDO space is freed.
But this is not the case, the usage vdostats --hu does not change
I am using

        issue_discards = 1
        thin_pool_discards = "passdown"
        thin_pool_zero = 1

therefore discards should be passed down to VDO

lvs -o  name,discards
  LV                 Discards
  lvroot                     
  lvswap                     
  lvvar                      
  lv_data_pool       passdown
  lv_data_vdo_vpool0         
  lvdata             passdown
  lvdata_s1          passdown

Therefore the space of deleted snapshots continuously cumulate, and at some point the VDO volume runs out of space, even if I create only some data and all thin snapshots are deleted.

How can I free VDO space, when I delete an thin-snapshot of a thin volume on top of VDO.

Regards

Hansjörg

[zkabelac]

Yep - this feature is still in devel ATM - there are more troubles along this route.
Meanwhile - until resolved - you can run 'blkdiscard /dev/vg/lv' before dropping thin volume.

[nova-2nd]

Hi

I am kind of in the same boat, but worse.
For me discards are not happening at all, neither fstrim, blkdiscard nor deleting lv...

LVM2 2.03.30
Linux 6.13.2-arch1-1

Regards,
Stefan