[linux-lvm] unable to remove snapshot of raid1 leg

[Heinz Mauelshagen]

Hi Alexander,

LVM snapshots are meant to be used on the user visible raid1 LVs.
You found a bug allowing it to be used on its hidden legs.

Removing such per leg snapshot should be possible after the raid1 LV got 
deactivated.

Heinz


On 10/23/2017 04:19 PM, Alexander 'Leo' Bergolth wrote:
> Hi!
>
> As the raid1 check of my two-drive LV recently reported a mismatch count
>> 0, I did some forensics.
> One experiment was to create a snapshot of one leg of the mirror and try
> to mount the snapshot. This worked fine but unfortunately I cannot
> remove the snapshot now!
>
> lvm wants to remove the origin too:
> -------------------- 8< --------------------
> # lvremove vg_test/snap_leg_0
> Do you really want to remove active origin logical volume vg_test/testlv_rimage_0 with 1 snapshot(s)? [y/n]: n
>    Logical volume vg_test/testlv_rimage_0 not removed.
> -------------------- 8< --------------------
> (I have added the full history of a test setup below.)
>
> Could anyone provide a hint how to get rid of the snapshot?
> (Maybe manually using dmsetup commands and metadata backup editing?)
>
> Thanks,
> --leo
>
> -------------------- snip! --------------------
> # lvcreate --type raid1 -m 1 -n testlv -L100m vg_test /dev/vdb /dev/vdc
>    Logical volume "testlv" created.
> # lvcreate -s -L50m -n snap_leg_0 /dev/mapper/vg_test-testlv_rimage_0
>    Using default stripesize 64.00 KiB.
>    Rounding up size to full physical extent 52.00 MiB
>    Logical volume "snap_leg_0" created.
>
> # lvremove vg_test/snap_leg_0
> Do you really want to remove active origin logical volume vg_test/testlv_rimage_0 with 1 snapshot(s)? [y/n]: n
>    Logical volume vg_test/testlv_rimage_0 not removed.
>
> # lvs -a -o+devices,lv_uuid
>    LV                VG      Attr       LSize   Pool Origin            Data%  Meta%  Move Log Cpy%Sync Convert Devices                               LV UUID
>    root              vg_sys  -wi-ao----   5.00g                                                                /dev/vda2(0)                          fqp4Np-mLyL-y0OS-nufS-0hsT-7ijc-lGD9Za
>    swap              vg_sys  -wi-ao----   2.00g                                                                /dev/vda2(2048)                       uNG1ht-eOKQ-y8Ji-yWSU-ZkZS-ZTIe-1M82mW
>    var               vg_sys  -wi-ao----   3.00g                                                                /dev/vda2(1280)                       nDwCsP-vn38-6AUb-Dqer-VkLv-QHs3-CfVNCR
>    snap_leg_0        vg_test swi-a-s---  52.00m      [testlv_rimage_0] 0.00                                    /dev/vdb(26)                          f5AXqK-lDNe-hNrO-AW7G-yFvl-ctxU-fivKQf
>    testlv            vg_test rwi-a-r--- 100.00m                                               100.00           testlv_rimage_0(0),testlv_rimage_1(0) Av5Y8Z-NBTH-tfN2-hCbW-Sur0-ebGU-SHBlsk
>    [testlv_rimage_0] vg_test owi-aor--- 100.00m                                                                /dev/vdb(1)                           OJyEep-Lgfm-B20o-4rfl-d38O-QByz-8oBa5z
>    [testlv_rimage_1] vg_test iwi-aor--- 100.00m                                                                /dev/vdc(1)                           J4AP4p-Mhfo-4oPn-SOFP-CGAi-riyL-CFr1fk
>    [testlv_rmeta_0]  vg_test ewi-aor---   4.00m                                                                /dev/vdb(0)                           Hgd58x-5Z2C-phkD-cIvl-KbPB-UWPz-THyZ3h
>    [testlv_rmeta_1]  vg_test ewi-aor---   4.00m                                                                /dev/vdc(0)                           mvehrT-Ofci-nWpm-A43m-iBpl-YW1U-Z1Z9x4
>
> # lvremove --select lv_uuid=f5AXqK-lDNe-hNrO-AW7G-yFvl-ctxU-fivKQf
> Do you really want to remove active origin logical volume vg_test/testlv_rimage_0 with 1 snapshot(s)? [y/n]: n
>    Logical volume vg_test/testlv_rimage_0 not removed.
> -------------------- snip! --------------------
>
>