Bug 979631

(In reply to Corey Marthaler from comment #0)
> Description of problem:
> One of the thin pool test test cases is:
> 
> - [STS TODO]no drop of external origin keeping thin snap of it
> 
> Which Heinz said means: "It shouldn't be possible to remove an external
> origin _whilst_ one or more snapshots refer to it."


yes 'external origin' must be kept intact in all cases 
(only 'read-only' activation is allowed)
But there is possibly some minor misunderstanding which LV is 'external origin'.
It's the LV providing data for unprovisioned areas.

> 
> However it appears the is possible to do just that. Is this expected
> behavior?
> 
> # REMOVE THE CONVERTED EXT ORIGIN VOLUME
> SCENARIO - [remove_origin_under_snap]
> Create a snapshot and then attempt to remove it's origin
> Making origin volume
> lvcreate --thinpool POOL -L 1G snapper_thinp
> Sanity checking pool device metadata
> (thin_check /dev/mapper/snapper_thinp-POOL_tmeta)
> Create LV to be used as an EXTERNAL origin device
> lvcreate -L 1G -n origin snapper_thinp
> Converting LV into an external thin origin device
> lvconvert --thinpool snapper_thinp/POOL --originname extorigin -T origin

Converts 'origin' volume into  'extorigin'
and  'origin' itself will become as a regular writable thin volume.

> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other1
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other2
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other3
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other4
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other5
> Making snapshot of origin volume
> lvcreate -s /dev/snapper_thinp/origin -n remove_origin_under_snap
> Attempt to remove origin volume
> 
> [root@qalvm-01 ~]# lvs -a -o +devices
>   LV                       Attr      LSize  Pool Origin    Data%  Devices
>   POOL                     twi-a-tz-  1.00g                  0.00
> POOL_tdata(0)
>   [POOL_tdata]             Twi-ao---  1.00g                     /dev/vdh1(0)
>   [POOL_tmeta]             ewi-ao---  4.00m                     /dev/vdd1(0)
>   extorigin                ori------  1.00g                     /dev/vdg1(0)
  ^^^^^^^^^^^^
This volume is external origin (in lvm2's terminology)

>   origin                   Vwi-a-tz-  1.00g POOL extorigin   0.00
   ^^^^^^^^^
Thin volume which is using external origin 'extorigin'

>   other1                   Vwi-a-tz-  1.00g POOL             0.00
>   other2                   Vwi-a-tz-  1.00g POOL             0.00
>   other3                   Vwi-a-tz-  1.00g POOL             0.00
>   other4                   Vwi-a-tz-  1.00g POOL             0.00
>   other5                   Vwi-a-tz-  1.00g POOL             0.00
>   remove_origin_under_snap Vwi-a-tz-  1.00g POOL origin      0.00
> 
> # ATTEMPT TO REMOVE THE "CONVERTED" EXT ORIGIN:
> [root@qalvm-01 ~]# lvremove snapper_thinp/extorigin
> Removing external origin "extorigin" will remove 2 dependent volume(s).
> Proceed? [y/n]: y
> Do you really want to remove active logical volume origin? [y/n]: y
>   Logical volume "origin" successfully removed
> Do you really want to remove active logical volume remove_origin_under_snap?
> [y/n]: y
>   Logical volume "remove_origin_under_snap" successfully removed
>   Logical volume "extorigin" successfully removed

Tools knows the dependency and gives the user a choice to remove all related volumes.

Removal of external origin 'extorigin' triggers removal of 2 related thin volumes - 'origin' and 'remove_origin_under_snap' which both needs external origin for showing data from unprovisioned blocks.


> 
> [root@qalvm-01 ~]# lvs -a -o +devices
>   LV           Attr      LSize  Pool Origin Data%  Devices
>   POOL         twi-a-tz-  1.00g               0.00 POOL_tdata(0)
>   [POOL_tdata] Twi-ao---  1.00g                    /dev/vdh1(0)
>   [POOL_tmeta] ewi-ao---  4.00m                    /dev/vdd1(0)
>   other1       Vwi-a-tz-  1.00g POOL          0.00
>   other2       Vwi-a-tz-  1.00g POOL          0.00
>   other3       Vwi-a-tz-  1.00g POOL          0.00
>   other4       Vwi-a-tz-  1.00g POOL          0.00
>   other5       Vwi-a-tz-  1.00g POOL          0.00
> 
> 
> 
> # REMOVE THE PHYSICAL EXT ORIGIN VOLUME
> SCENARIO - [remove_origin_under_snap]
> Create a snapshot and then attempt to remove it's origin
> Making origin volume
> lvcreate --thinpool POOL -L 1G snapper_thinp
>   device-mapper: remove ioctl on  failed: Device or resource busy
> Sanity checking pool device metadata
> (thin_check /dev/mapper/snapper_thinp-POOL_tmeta)
> Create LV to be used as an EXTERNAL origin device
> lvcreate -L 1G -n origin snapper_thinp
> Converting LV into an external thin origin device
> lvconvert --thinpool snapper_thinp/POOL --originname extorigin -T origin
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other1
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other2
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other3
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other4
> lvcreate --virtualsize 1G --thinpool snapper_thinp/POOL -n other5
> Making snapshot of origin volume
> lvcreate -s /dev/snapper_thinp/origin -n remove_origin_under_snap
> Attempt to remove origin volume
> 
> [root@qalvm-01 ~]# lvs -a -o +devices
>   LV                       Attr      LSize  Pool Origin    Data%  Devices
>   POOL                     twi-a-tz-  1.00g                  0.00
> POOL_tdata(0)
>   [POOL_tdata]             Twi-ao---  1.00g                      
> /dev/vdh1(0)
>   [POOL_tmeta]             ewi-ao---  4.00m                      
> /dev/vdd1(0)
>   extorigin                ori------  1.00g                      
> /dev/vdg1(0)
>   origin                   Vwi-a-tz-  1.00g POOL extorigin   0.00
>   other1                   Vwi-a-tz-  1.00g POOL             0.00
>   other2                   Vwi-a-tz-  1.00g POOL             0.00
>   other3                   Vwi-a-tz-  1.00g POOL             0.00
>   other4                   Vwi-a-tz-  1.00g POOL             0.00
>   other5                   Vwi-a-tz-  1.00g POOL             0.00
>   remove_origin_under_snap Vwi-a-tz-  1.00g POOL origin      0.00
> 
> # ATTEMPT TO REMOVE THE "PHYSICAL" EXT ORIGIN:
> [root@qalvm-01 ~]# lvremove snapper_thinp/origin
> Do you really want to remove active logical volume origin? [y/n]: y
>   Logical volume "origin" successfully removed

yep - here is no problem with removal of 'origin' volume.

> [root@qalvm-01 ~]# lvs -a -o +devices
>   LV                       Attr      LSize  Pool Origin    Data%  Devices
>   POOL                     twi-a-tz-  1.00g                  0.00
> POOL_tdata(0)
>   [POOL_tdata]             Twi-ao---  1.00g                      /dev/vdh1(0)
>   [POOL_tmeta]             ewi-ao---  4.00m                      /dev/vdd1(0)
>   extorigin                ori------  1.00g                      /dev/vdg1(0)
>   other1                   Vwi-a-tz-  1.00g POOL             0.00
>   other2                   Vwi-a-tz-  1.00g POOL             0.00
>   other3                   Vwi-a-tz-  1.00g POOL             0.00
>   other4                   Vwi-a-tz-  1.00g POOL             0.00
>   other5                   Vwi-a-tz-  1.00g POOL             0.00
>   remove_origin_under_snap Vwi-a-tz-  1.00g POOL extorigin   0.00

Removed 'origin' volume is now replaced with external origin 'extorigin' volume directly. 
So this VG has 1 external origin LV - 'extorigin'  and 1 thin volume 'remove_origin_under_snap' which is it for unprovisioned areas.

Hopefully clear.

Note - you could create very long chain of external origins even between different pools - however the usability and understandability of such metadata and table mapping is questionable....