KVM, libvirt, and LVs inside LVs

Question

I have a Debian server running KVM+libvirt. The VMs disks are LVs on the host. The trouble is that if I create LVs inside the guests, they are recursively detected on the host and that creates all sort of problems, like the inability to resize or delete properly LVs.

So I added a filter rule to /etc/lvm/lvm.conf like this, to exclude scanning LVs inside other LVs:

filter = [ "r|/dev/dm-*|", "a|/dev/sd.*|" ]

Now my problem is : how do I get LVM to rescan only the "real" VGs and LVs? I now have errors like this:

# lvs
  WARNING: Device for PV 73C0Ma-sAYV-Aa10-pAHB-ZAZA-3QjH-Rk1eTS not found or rejected by a filter.
  WARNING: Device for PV fcEG5k-BLzO-dbAr-Yw8o-dPw2-1hAk-VyluvW not found or rejected by a filter.
  LV              VG              Attr       LSize    Pool Origin    Data%  Meta%  Move Log Cpy%Sync Convert
  HaProxy         data            -wi-ao----   20,00g                                                       
  backup          data            -wi-ao----    4,00t                                                       
  database        data            -wi-ao----   16,00g                                                       
  lvol0           data            swi-a-s---   16,07g      stone-web 70,43                                  
  stone-vtls      data            -wi-ao----    2,00t                                                       
  stone-web       data            owi-aos---   16,00g                                                       
  lv0             ftpstorage      -wi-----p-   10,00t

The last lv in this case is actually a LV from a VM, not from the host... How do I get rid of it without rebooting the host?

could you provide some informations about your physical volumes? what kind of disk backend are you using as disk for the vm? — c4f4t0r, Feb 29 '20 at 23:36
There is a RAID array used as pv for the vg, split in lvs. The lvs are the disks for the VMs (using virtio). — wazoox, Mar 01 '20 at 14:52
but in your quenstion, include the output of pvs in the physical host — c4f4t0r, Mar 01 '20 at 16:23

hargut · Accepted Answer · 2020-03-01T13:49:26.103

4

As per pvscan man page and RHEL documentation the following should work: /etc/lvm/lvm.conf

global_filter = [ "r|/dev/dm-*|", "a|/dev/sd.*|" ]

pvscan --cache

https://www.systutorials.com/docs/linux/man/8-pvscan/

To prevent devices from being scanned by pvscan --cache,
add them to lvm.conf(5) devices/global_filter.
The devices/filter setting does not apply to system level
scanning. For more information, see:
    lvmconfig --withcomments devices/global_filter

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/lvm_filters

edited Mar 01 '20 at 13:49

answered Mar 01 '20 at 10:50

hargut

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I've tried pvscan --cache, pvscan, vgscan -ay and vgscan -an, no dice. lvs, vgs still outputs the same error. – wazoox Mar 01 '20 at 14:51
Did you update your config to `global_filter` instead of `filter`? What does `lvm dumpconfig` show? – hargut Mar 01 '20 at 16:02
How does the output of `blkid` look like? – hargut Mar 01 '20 at 16:12
Ah yes my bad, with global_filter the problem is solved! – wazoox Mar 01 '20 at 21:00

KVM, libvirt, and LVs inside LVs

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