[lvm-devel] lvmcache lv destroy with no flush

[Zdenek Kabelac]

Dne 02. 08. 19 v 16:24 Lakshmi Narasimhan Sundararajan napsal(a):
>   * 1.) remove devices from DM table
>   * dmsetup remove_all
>   * (or just some selected device - whatever fits...)
>   *
>   * 2.) remove disk singatures of VG
>   * wipefs -a /dev/sdc
>   * wipefs -a /dev/nvme0n1
>   * (or pvremove -ff /dev/sdc /dev/nvme0n1)
>   *
>   * 3.) recreate empty VG from scratch
>   * vgcreate pxtest /dev/sdc /dev/nvme0n1
> 
> myhome$ sudo dmsetup status --target cache
> 
> pxtest-pool: 0 20963328 cache 8 40/2048 2048 4096/10220 28 58 0 0 0 0 4096 1 
> writethrough 2 migration_threshold 2048 cleaner 0 rw -
> 
> myhome$ sudo dmsetup remove pxtest-pool


Unfortunatelly you must remove ALL related device.


>    0 logical volume(s) in volume group "pxtest" now active
> 
> myhome$ sudo pvremove -ff /dev/sdc /dev/nvme0n1
> 
> Really WIPE LABELS from physical volume "/dev/sdc" of volume group "pxtest" 
> [y/n]? y
> 
>    WARNING: Wiping physical volume label from /dev/sdc of volume group "pxtest"
> 
>    Can't open /dev/sdc exclusively - not removing. Mounted filesystem?

As you can see - you still have some device holding sdc open.

As said origin - all used of  your SDC & NVME device must be removed - so 
devices are 'free'.

You can't be killing VG while DM device are still running in memory.

> 
> Really WIPE LABELS from physical volume "/dev/nvme0n1" of volume group 
> "pxtest" [y/n]? y
> 
>    WARNING: Wiping physical volume label from /dev/nvme0n1 of volume group 
> "pxtest"
> 
>    Can't open /dev/nvme0n1 exclusively - not removing. Mounted filesystem?
> 
> myhome$
> 
> myhome$ sudo wipefs -a /dev/sdc /dev/nvme0n1
> 
> wipefs: error: /dev/sdc: probing initialization failed: Device or resource busy
> 
> myhome$
> 
> Doesn’t seem to work, there are still exclusive references on the drive held 
> by lvm!


Note - lvm2 never helds ANY reference - lvm2 is pure tool for manipulation 
with DM devices - aka you can do those DM devices yourself without any lvm2 in 
place - it's just way more work.

So back to question who keeps devices open - you can easily get this info from 
command like these:


dmsetup table

dmsetup ls --tree

lsbls
...


Before you start any device wiping for VG metadata - there must be no runing 
device holding those device open - and as you are basically bypassing lvm2 
when you run 'drastic' commands like 'dmsetup' or 'wipefs' yourself - you 
can't blame lvm2 for not being cooperative for such 'violence' usage :)
As has been originally said - advice was serious HACK in the lvm2 workflow....

Regards

Zdenek