Delete custom Storage/Volume fail

Hello, I have weird problem on deleting a custom Storage/Volume.
The storage is a nested LVM/xfs, whitout thinpool and snap set lxd lvm.external=true.

I detach the volume from the container. Randomly I have this error:

lxc storage volume detach ssd mmostBleve mattermost
Error: Failed to stop device "mmostBleve": Failed to deactivate LVM logical volume "/dev/lxd-ssd/custom_default_mmostBleve": Failed to run: lvchange --activate n --ignoreactivationskip /dev/lxd-ssd/custom_default_mmostBleve: exit status 5 (Logical volume lxd-ssd/custom_default_mmostBleve contains a filesystem in use.)

With, or without, error inside the container the volume is unmounted. In case of error a second try work without error.

At this point I try to delete the volume and I always have the previous error:

lxc storage volume delete ssd mmostBleve
Error: Error removing LVM logical volume: Failed to run: lvremove -f /dev/lxd-ssd/custom_default_mmostBleve: exit status 5 (Logical volume lxd-ssd/custom_default_mmostBleve contains a filesystem in use.)

I checked with several tool how is using this device without success (lsof, /proc/*/mountinfo, fuser, … )

Some one can help me?

Here the lxc info output

config:
  core.https_address: '[::]:8443'
  core.trust_password: true
api_extensions:
- storage_zfs_remove_snapshots
- container_host_shutdown_timeout
- container_stop_priority
- container_syscall_filtering
- auth_pki
- container_last_used_at
- etag
- patch
- usb_devices
- https_allowed_credentials
- image_compression_algorithm
- directory_manipulation
- container_cpu_time
- storage_zfs_use_refquota
- storage_lvm_mount_options
- network
- profile_usedby
- container_push
- container_exec_recording
- certificate_update
- container_exec_signal_handling
- gpu_devices
- container_image_properties
- migration_progress
- id_map
- network_firewall_filtering
- network_routes
- storage
- file_delete
- file_append
- network_dhcp_expiry
- storage_lvm_vg_rename
- storage_lvm_thinpool_rename
- network_vlan
- image_create_aliases
- container_stateless_copy
- container_only_migration
- storage_zfs_clone_copy
- unix_device_rename
- storage_lvm_use_thinpool
- storage_rsync_bwlimit
- network_vxlan_interface
- storage_btrfs_mount_options
- entity_description
- image_force_refresh
- storage_lvm_lv_resizing
- id_map_base
- file_symlinks
- container_push_target
- network_vlan_physical
- storage_images_delete
- container_edit_metadata
- container_snapshot_stateful_migration
- storage_driver_ceph
- storage_ceph_user_name
- resource_limits
- storage_volatile_initial_source
- storage_ceph_force_osd_reuse
- storage_block_filesystem_btrfs
- resources
- kernel_limits
- storage_api_volume_rename
- macaroon_authentication
- network_sriov
- console
- restrict_devlxd
- migration_pre_copy
- infiniband
- maas_network
- devlxd_events
- proxy
- network_dhcp_gateway
- file_get_symlink
- network_leases
- unix_device_hotplug
- storage_api_local_volume_handling
- operation_description
- clustering
- event_lifecycle
- storage_api_remote_volume_handling
- nvidia_runtime
- container_mount_propagation
- container_backup
- devlxd_images
- container_local_cross_pool_handling
- proxy_unix
- proxy_udp
- clustering_join
- proxy_tcp_udp_multi_port_handling
- network_state
- proxy_unix_dac_properties
- container_protection_delete
- unix_priv_drop
- pprof_http
- proxy_haproxy_protocol
- network_hwaddr
- proxy_nat
- network_nat_order
- container_full
- candid_authentication
- backup_compression
- candid_config
- nvidia_runtime_config
- storage_api_volume_snapshots
- storage_unmapped
- projects
- candid_config_key
- network_vxlan_ttl
- container_incremental_copy
- usb_optional_vendorid
- snapshot_scheduling
- snapshot_schedule_aliases
- container_copy_project
- clustering_server_address
- clustering_image_replication
- container_protection_shift
- snapshot_expiry
- container_backup_override_pool
- snapshot_expiry_creation
- network_leases_location
- resources_cpu_socket
- resources_gpu
- resources_numa
- kernel_features
- id_map_current
- event_location
- storage_api_remote_volume_snapshots
- network_nat_address
- container_nic_routes
- rbac
- cluster_internal_copy
- seccomp_notify
- lxc_features
- container_nic_ipvlan
- network_vlan_sriov
- storage_cephfs
- container_nic_ipfilter
- resources_v2
- container_exec_user_group_cwd
- container_syscall_intercept
- container_disk_shift
- storage_shifted
- resources_infiniband
- daemon_storage
- instances
- image_types
- resources_disk_sata
- clustering_roles
- images_expiry
- resources_network_firmware
- backup_compression_algorithm
- ceph_data_pool_name
- container_syscall_intercept_mount
- compression_squashfs
- container_raw_mount
- container_nic_routed
- container_syscall_intercept_mount_fuse
- container_disk_ceph
- virtual-machines
- image_profiles
- clustering_architecture
- resources_disk_id
- storage_lvm_stripes
- vm_boot_priority
- unix_hotplug_devices
- api_filtering
- instance_nic_network
- clustering_sizing
- firewall_driver
- projects_limits
- container_syscall_intercept_hugetlbfs
- limits_hugepages
- container_nic_routed_gateway
- projects_restrictions
- custom_volume_snapshot_expiry
- volume_snapshot_scheduling
- trust_ca_certificates
- snapshot_disk_usage
- clustering_edit_roles
- container_nic_routed_host_address
- container_nic_ipvlan_gateway
- resources_usb_pci
- resources_cpu_threads_numa
- resources_cpu_core_die
- api_os
- container_nic_routed_host_table
- container_nic_ipvlan_host_table
- container_nic_ipvlan_mode
- resources_system
- images_push_relay
- network_dns_search
- container_nic_routed_limits
- instance_nic_bridged_vlan
- network_state_bond_bridge
- usedby_consistency
- custom_block_volumes
- clustering_failure_domains
- resources_gpu_mdev
- console_vga_type
- projects_limits_disk
- network_type_macvlan
- network_type_sriov
- container_syscall_intercept_bpf_devices
- network_type_ovn
- projects_networks
- projects_networks_restricted_uplinks
- custom_volume_backup
- backup_override_name
- storage_rsync_compression
- network_type_physical
- network_ovn_external_subnets
- network_ovn_nat
- network_ovn_external_routes_remove
- tpm_device_type
- storage_zfs_clone_copy_rebase
- gpu_mdev
- resources_pci_iommu
- resources_network_usb
- resources_disk_address
- network_physical_ovn_ingress_mode
- network_ovn_dhcp
- network_physical_routes_anycast
- projects_limits_instances
- network_state_vlan
- instance_nic_bridged_port_isolation
- instance_bulk_state_change
- network_gvrp
- instance_pool_move
- gpu_sriov
- pci_device_type
- storage_volume_state
- network_acl
- migration_stateful
- disk_state_quota
- storage_ceph_features
- projects_compression
- projects_images_remote_cache_expiry
- certificate_project
- network_ovn_acl
- projects_images_auto_update
- projects_restricted_cluster_target
- images_default_architecture
- network_ovn_acl_defaults
- gpu_mig
- project_usage
- network_bridge_acl
- warnings
- projects_restricted_backups_and_snapshots
- clustering_join_token
- clustering_description
- server_trusted_proxy
- clustering_update_cert
- storage_api_project
- server_instance_driver_operational
- server_supported_storage_drivers
- event_lifecycle_requestor_address
- resources_gpu_usb
- clustering_evacuation
- network_ovn_nat_address
- network_bgp
- network_forward
- custom_volume_refresh
- network_counters_errors_dropped
- metrics
- image_source_project
- clustering_config
- network_peer
- linux_sysctl
- network_dns
- ovn_nic_acceleration
- certificate_self_renewal
- instance_project_move
- storage_volume_project_move
- cloud_init
- network_dns_nat
- database_leader
- instance_all_projects
- clustering_groups
- ceph_rbd_du
- instance_get_full
- qemu_metrics
- gpu_mig_uuid
- event_project
- clustering_evacuation_live
- instance_allow_inconsistent_copy
- network_state_ovn
- storage_volume_api_filtering
- image_restrictions
- storage_zfs_export
- network_dns_records
- storage_zfs_reserve_space
- network_acl_log
- storage_zfs_blocksize
- metrics_cpu_seconds
- instance_snapshot_never
- certificate_token
- instance_nic_routed_neighbor_probe
- event_hub
- agent_nic_config
- projects_restricted_intercept
- metrics_authentication
- images_target_project
- cluster_migration_inconsistent_copy
- cluster_ovn_chassis
- container_syscall_intercept_sched_setscheduler
- storage_lvm_thinpool_metadata_size
- storage_volume_state_total
- instance_file_head
- instances_nic_host_name
- image_copy_profile
- container_syscall_intercept_sysinfo
- clustering_evacuation_mode
- resources_pci_vpd
- qemu_raw_conf
- storage_cephfs_fscache
- network_load_balancer
- vsock_api
- instance_ready_state
- network_bgp_holdtime
- storage_volumes_all_projects
- metrics_memory_oom_total
- storage_buckets
- storage_buckets_create_credentials
- metrics_cpu_effective_total
- projects_networks_restricted_access
- storage_buckets_local
- loki
- acme
- internal_metrics
- cluster_join_token_expiry
- remote_token_expiry
- init_preseed
- storage_volumes_created_at
- cpu_hotplug
- projects_networks_zones
- network_txqueuelen
- cluster_member_state
- instances_placement_scriptlet
- storage_pool_source_wipe
- zfs_block_mode
- instance_generation_id
- disk_io_cache
- amd_sev
- storage_pool_loop_resize
- migration_vm_live
- ovn_nic_nesting
- oidc
- network_ovn_l3only
- ovn_nic_acceleration_vdpa
- cluster_healing
- instances_state_total
- auth_user
- security_csm
- instances_rebuild
- numa_cpu_placement
api_status: stable
api_version: "1.0"
auth: trusted
public: false
auth_methods:
- tls
auth_user_name: root
auth_user_method: unix
environment:
  addresses:
  - <removed>
  architectures:
  - x86_64
  - i686
  certificate: |
    -----BEGIN CERTIFICATE-----
    MIICBDCCAYqgAwIBAgIRAKssyIeYYTER61GjlYQb9OwwCgYIKoZIzj0EAwMwNDEc
    MBoGA1UEChMTbGludXhjb250YWluZXJzLm9yZzEUMBIGA1UEAwwLcm9vdEBvdmgt
    bDIwHhcNMTkxMjAzMTU0OTE2WhcNMjkxMTMwMTU0OTE2WjA0MRwwGgYDVQQKExNs
    aW51eGNvbnRhaW5lcnMub3JnMRQwEgYDVQQDDAtyb290QG92aC1sMjB2MBAGByqG
    SM49AgEGBSuBBAAiA2IABO1KVvQj4YaLw/wbe+JW2SUe6k0InQQZVzVxlulmFBgQ
    MXM+QqgssAYzxvOcbQtnNB8yEyPbQtbnJPCPx93+LaCWCxoM6NXhgW/DJLvJe2Bm
    Ta0Jv/MXahS7rgUmETX6h6NgMF4wDgYDVR0PAQH/BAQDAgWgMBMGA1UdJQQMMAoG
    CCsGAQUFBwMBMAwGA1UdEwEB/wQCMAAwKQYDVR0RBCIwIIIGb3ZoLWwyhwQlu1kt
    hxAgAUHQAAoxLQAAAAAAAAAAMAoGCCqGSM49BAMDA2gAMGUCMGWZdREVyusIZXwZ
    AWqPgP9QQaXhipyJrufHSCEqc6hOGgXupf4vj4yaK9Ar84Y9VwIxAILq7KsT8zxn
    ZKmY5xsMsa/0EGnF8s0aix1zjv0R3kBlIG71qEjV25i5y+1gbTbRRg==
    -----END CERTIFICATE-----
  certificate_fingerprint: e7b1e9437b2d2c06118a38c9941a8406c27426ff082dfca52600573c64dbc472
  driver: lxc | qemu
  driver_version: 5.0.2 | 8.0.0
  firewall: xtables
  kernel: Linux
  kernel_architecture: x86_64
  kernel_features:
    idmapped_mounts: "false"
    netnsid_getifaddrs: "false"
    seccomp_listener: "false"
    seccomp_listener_continue: "false"
    shiftfs: "false"
    uevent_injection: "false"
    unpriv_fscaps: "true"
  kernel_version: 4.15.0-161-generic
  lxc_features:
    cgroup2: "true"
    core_scheduling: "true"
    devpts_fd: "true"
    idmapped_mounts_v2: "true"
    mount_injection_file: "true"
    network_gateway_device_route: "true"
    network_ipvlan: "true"
    network_l2proxy: "true"
    network_phys_macvlan_mtu: "true"
    network_veth_router: "true"
    pidfd: "true"
    seccomp_allow_deny_syntax: "true"
    seccomp_notify: "true"
    seccomp_proxy_send_notify_fd: "true"
  os_name: Ubuntu
  os_version: "18.04"
  project: default
  server: lxd
  server_clustered: false
  server_event_mode: full-mesh
  server_name: ovh-l2
  server_pid: 14370
  server_version: "5.15"
  storage: lvm
  storage_version: 2.02.176(2) (2017-11-03) / 1.02.145 (2017-11-03) / 4.37.0
  storage_supported_drivers:
  - name: ceph
    version: 17.2.5
    remote: true
  - name: cephfs
    version: 17.2.5
    remote: true
  - name: cephobject
    version: 17.2.5
    remote: true
  - name: dir
    version: "1"
    remote: false
  - name: lvm
    version: 2.02.176(2) (2017-11-03) / 1.02.145 (2017-11-03) / 4.37.0
    remote: false
  - name: btrfs
    version: 5.16.2
    remote: false

Can you show the output of the command below with the container stopped:

sudo LD_LIBRARY_PATH=/snap/lxd/current/lib/:/snap/lxd/current/lib/x86_64-linux-gnu/ nsenter --mount=/run/snapd/ns/lxd.mnt -- findmnt

Hi Tomp, thank you for your reply.

I have run the command but have not stopped any containers (I have to plan for this). In any case, the non-deletable volume is not assigned to any container.

TARGET                                                    SOURCE                         FSTYPE      OPTIONS
/                                                         none                           tmpfs       rw,relatime,gid=1000
├─/README.md                                              /dev/loop42[/README.md]        squashfs    ro,nodev,relatime
├─/boot                                                   /dev/loop42[/boot]             squashfs    ro,nodev,relatime
│ └─/boot                                                 /dev/md1                       ext4        rw,relatime,discard,errors=remount-ro,stripe=4,data=ordered
├─/copyright                                              /dev/loop42[/copyright]        squashfs    ro,nodev,relatime
├─/host                                                   /dev/loop42[/host]             squashfs    ro,nodev,relatime
├─/meta                                                   /dev/loop42[/meta]             squashfs    ro,nodev,relatime
├─/opt                                                    /dev/loop42[/opt]              squashfs    ro,nodev,relatime
├─/srv                                                    /dev/loop42[/srv]              squashfs    ro,nodev,relatime
├─/usr                                                    /dev/loop42[/usr]              squashfs    ro,nodev,relatime
│ ├─/usr/bin/kmod                                         /dev/loop40[/wrappers/kmod]    squashfs    ro,nodev,relatime
│ ├─/usr/share/ca-certificates                            /dev/md2[/usr/share/ca-certificates]
│ │                                                                                      xfs         rw,relatime,attr2,inode64,noquota
│ ├─/usr/share/misc                                       tmpfs                          tmpfs       rw,relatime,mode=755
│ ├─/usr/lib/modules                                      /dev/md2[/lib/modules]         xfs         rw,relatime,attr2,inode64,noquota
│ ├─/usr/lib/firmware                                     /dev/md2[/lib/firmware]        xfs         rw,relatime,attr2,inode64,noquota
│ ├─/usr/src                                              /dev/md2[/usr/src]             xfs         rw,relatime,attr2,inode64,noquota
│ └─/usr/lib/snapd                                        /dev/loop35[/usr/lib/snapd]    squashfs    ro,nodev,relatime
├─/var                                                    /dev/loop42[/var]              squashfs    ro,nodev,relatime
│ ├─/var/snap                                             /dev/md2[/var/snap]            xfs         rw,relatime,attr2,inode64,noquota
│ │ ├─/var/snap/lxd/common/lxd/storage-pools              /dev/md2[/var/snap/lxd/common/lxd/storage-pools]
│ │ │                                                                                    xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/mgnlICML
│ │ │ │                                                   /dev/lxd/containers_mgnlICML   xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/mmost-imgproxy
│ │ │ │                                                   /dev/lxd/containers_mmost--imgproxy
│ │ │ │                                                                                  xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/redis
│ │ │ │                                                   /dev/lxd/containers_redis      xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/voceEvangelica
│ │ │ │                                                   /dev/lxd/containers_voceEvangelica
│ │ │ │                                                                                  xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/docker
│ │ │ │                                                   /dev/lxd/containers_docker     xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/custom/default_dokRepo
│ │ │ │                                                   /dev/lxd/custom_default_dokRepo
│ │ │ │                                                                                  xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/custom/default_docker
│ │ │ │                                                   /dev/lxd/custom_default_docker xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/energia-abm
│ │ │ │                                                   /dev/lxd/containers_energia--abm
│ │ │ │                                                                                  xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/postgres
│ │ │ │                                                   /dev/lxd/containers_postgres   xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/wikijs
│ │ │ │                                                   /dev/lxd/containers_wikijs     xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/ssd/custom/default_wikiJSpostgres
│ │ │ │                                                   /dev/lxd-ssd/custom_default_wikiJSpostgres
│ │ │ │                                                                                  xfs         rw,relatime,attr2,discard,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/dns01
│ │ │ │                                                   /dev/lxd/containers_dns01      xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/mysql
│ │ │ │                                                   /dev/lxd/containers_mysql      xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/ssd/custom/default_mysqldata
│ │ │ │                                                   /dev/lxd-ssd/custom_default_mysqldata
│ │ │ │                                                                                  xfs         rw,relatime,attr2,discard,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/mysql8
│ │ │ │                                                   /dev/lxd/containers_mysql8     xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/ssd/custom/default_mysqldata8
│ │ │ │                                                   /dev/lxd-ssd/custom_default_mysqldata8
│ │ │ │                                                                                  xfs         rw,relatime,attr2,discard,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/containers/mattermost
│ │ │ │                                                   /dev/lxd/containers_mattermost xfs         rw,relatime,attr2,inode64,noquota
│ │ │ ├─/var/snap/lxd/common/lxd/storage-pools/default/custom/default_mmostData
│ │ │ │                                                   /dev/lxd/custom_default_mmostData
│ │ │ │                                                                                  xfs         rw,relatime,attr2,inode64,noquota
│ │ │ └─/var/snap/lxd/common/lxd/storage-pools/ssd/custom/default_mmostBleveIdx
│ │ │                                                     /dev/lxd-ssd/custom_default_mmostBleveIdx
│ │ │                                                                                    xfs         rw,relatime,attr2,discard,inode64,noquota
│ │ ├─/var/snap/lxd/common/lxd/devices                    /dev/md2[/var/snap/lxd/common/lxd/devices]
│ │ │                                                                                    xfs         rw,relatime,attr2,inode64,noquota
│ │ ├─/var/snap/lxd/common/lxd/devlxd                     tmpfs                          tmpfs       rw,relatime,size=100k,mode=755
│ │ ├─/var/snap/lxd/common/shmounts                       tmpfs                          tmpfs       rw,relatime,size=1024k,mode=711
│ │ │ ├─/var/snap/lxd/common/shmounts                     tmpfs                          tmpfs       rw,relatime,size=1024k,mode=711
│ │ │ │ └─/var/snap/lxd/common/shmounts/lxcfs             lxcfs                          fuse.lxcfs  rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other
│ │ │ ├─/var/snap/lxd/common/shmounts/lxcfs               lxcfs                          fuse.lxcfs  rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other
│ │ │ └─/var/snap/lxd/common/shmounts/instances           tmpfs                          tmpfs       rw,relatime,size=100k,mode=711
│ │ └─/var/snap/lxd/common/ns                             tmpfs                          tmpfs       rw,relatime,size=1024k,mode=700
│ ├─/var/lib/snapd                                        /dev/md2[/var/lib/snapd]       xfs         rw,relatime,attr2,inode64,noquota
│ │ └─/var/lib/snapd/hostfs                               /dev/md2[/var/lib/snapd/hostfs]
│ │                                                                                      xfs         rw,relatime,attr2,inode64,noquota
│ │   └─/var/lib/snapd/hostfs                             /dev/md2                       xfs         rw,relatime,attr2,inode64,noquota
│ │     ├─/var/lib/snapd/hostfs/snap/core20/2015          /dev/loop41                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/core18/2790          /dev/loop21                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/dev                       udev                           devtmpfs    rw,nosuid,relatime,size=16398484k,nr_inodes=4099621,mode=755
│ │     ├─/var/lib/snapd/hostfs/proc                      proc                           proc        rw,relatime
│ │     ├─/var/lib/snapd/hostfs/sys                       sysfs                          sysfs       rw,relatime
│ │     ├─/var/lib/snapd/hostfs/run                       tmpfs                          tmpfs       rw,nosuid,noexec,relatime,size=3284780k,mode=755
│ │     │ ├─/var/lib/snapd/hostfs/run/lock                tmpfs                          tmpfs       rw,nosuid,nodev,noexec,relatime,size=5120k
│ │     │ ├─/var/lib/snapd/hostfs/run/snapd/ns            tmpfs[/snapd/ns]               tmpfs       rw,nosuid,noexec,relatime,size=3284780k,mode=755
│ │     │ └─/var/lib/snapd/hostfs/run/user/1000           tmpfs                          tmpfs       rw,nosuid,nodev,relatime,size=3284776k,mode=700,uid=1000,gid=1000
│ │     ├─/var/lib/snapd/hostfs/boot                      /dev/md1                       ext4        rw,relatime,discard,errors=remount-ro,stripe=4,data=ordered
│ │     ├─/var/lib/snapd/hostfs/home                      /dev/mapper/vg--host-home      xfs         rw,relatime,attr2,inode64,noquota
│ │     │ └─/var/lib/snapd/hostfs/home/cryms_backup/store /dev/mapper/vg--host-bkpstore  xfs         rw,relatime,attr2,inode64,noquota
│ │     ├─/var/lib/snapd/hostfs/var/snap/lxd/common/ns    tmpfs                          tmpfs       rw,relatime,size=1024k,mode=700
│ │     ├─/var/lib/snapd/hostfs/snap/core18/2785          /dev/loop37                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/lxd/25086            /dev/loop38                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/core20/1974          /dev/loop39                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/core/15511           /dev/loop35                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/lxd/25112            /dev/loop40                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/core22/817           /dev/loop31                    squashfs    ro,nodev,relatime
│ │     ├─/var/lib/snapd/hostfs/snap/core22/858           /dev/loop42                    squashfs    ro,nodev,relatime
│ │     └─/var/lib/snapd/hostfs/snap/core/15925           /dev/loop36                    squashfs    ro,nodev,relatime
│ ├─/var/tmp                                              /dev/md2[/var/tmp]             xfs         rw,relatime,attr2,inode64,noquota
│ └─/var/log                                              /dev/md2[/var/log]             xfs         rw,relatime,attr2,inode64,noquota
├─/writable                                               /dev/loop42[/writable]         squashfs    ro,nodev,relatime
├─/dev                                                    udev                           devtmpfs    rw,nosuid,relatime,size=16398484k,nr_inodes=4099621,mode=755
│ ├─/dev/ptmx                                             devpts[/ptmx]                  devpts      rw,relatime,gid=5,mode=620,ptmxmode=666
│ ├─/dev/pts                                              devpts                         devpts      rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000
│ │ └─/dev/pts                                            devpts                         devpts      rw,relatime,gid=5,mode=620,ptmxmode=666
│ ├─/dev/shm                                              tmpfs                          tmpfs       rw,nosuid,nodev
│ ├─/dev/mqueue                                           mqueue                         mqueue      rw,relatime
│ └─/dev/hugepages                                        hugetlbfs                      hugetlbfs   rw,relatime,pagesize=2M
├─/etc                                                    /dev/md2[/etc]                 xfs         rw,relatime,attr2,inode64,noquota
│ ├─/etc                                                  tmpfs                          tmpfs       rw,relatime,mode=755
│ ├─/etc/nsswitch.conf                                    /dev/loop42[/etc/nsswitch.conf]
│ │                                                                                      squashfs    ro,nodev,relatime
│ ├─/etc/apparmor                                         /dev/loop42[/etc/apparmor]     squashfs    ro,nodev,relatime
│ └─/etc/apparmor.d                                       /dev/loop42[/etc/apparmor.d]   squashfs    ro,nodev,relatime
├─/home                                                   /dev/mapper/vg--host-home      xfs         rw,relatime,attr2,inode64,noquota
│ └─/home/cryms_backup/store                              /dev/mapper/vg--host-bkpstore  xfs         rw,relatime,attr2,inode64,noquota
├─/root                                                   /dev/md2[/root]                xfs         rw,relatime,attr2,inode64,noquota
├─/proc                                                   proc                           proc        rw,relatime
│ └─/proc/sys/fs/binfmt_misc                              systemd-1                      autofs      rw,relatime,fd=33,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_i
│   └─/proc/sys/fs/binfmt_misc                            binfmt_misc                    binfmt_misc rw,relatime
├─/sys                                                    sysfs                          sysfs       rw,relatime
│ ├─/sys/kernel/security                                  securityfs                     securityfs  rw,nosuid,nodev,noexec,relatime
│ ├─/sys/fs/cgroup                                        tmpfs                          tmpfs       ro,nosuid,nodev,noexec,mode=755
│ │ ├─/sys/fs/cgroup/unified                              cgroup                         cgroup2     rw,nosuid,nodev,noexec,relatime
│ │ ├─/sys/fs/cgroup/systemd                              cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,xattr,name=systemd
│ │ ├─/sys/fs/cgroup/freezer                              cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,freezer
│ │ ├─/sys/fs/cgroup/cpu,cpuacct                          cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,cpu,cpuacct
│ │ ├─/sys/fs/cgroup/hugetlb                              cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,hugetlb
│ │ ├─/sys/fs/cgroup/blkio                                cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,blkio
│ │ ├─/sys/fs/cgroup/memory                               cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,memory
│ │ ├─/sys/fs/cgroup/net_cls,net_prio                     cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,net_cls,net_prio
│ │ ├─/sys/fs/cgroup/devices                              cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,devices
│ │ ├─/sys/fs/cgroup/rdma                                 cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,rdma
│ │ ├─/sys/fs/cgroup/cpuset                               cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,cpuset,clone_children
│ │ ├─/sys/fs/cgroup/pids                                 cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,pids
│ │ └─/sys/fs/cgroup/perf_event                           cgroup                         cgroup      rw,nosuid,nodev,noexec,relatime,perf_event
│ ├─/sys/fs/pstore                                        pstore                         pstore      rw,nosuid,nodev,noexec,relatime
│ ├─/sys/kernel/debug                                     debugfs                        debugfs     rw,relatime
│ │ └─/sys/kernel/debug/tracing                           tracefs                        tracefs     rw,relatime
│ ├─/sys/kernel/config                                    configfs                       configfs    rw,relatime
│ └─/sys/fs/fuse/connections                              fusectl                        fusectl     rw,relatime
├─/tmp                                                    /dev/md2[/tmp]                 xfs         rw,relatime,attr2,inode64,noquota
│ └─/tmp                                                  /dev/md2[/tmp/snap-private-tmp/snap.lxd/tmp]
│                                                                                        xfs         rw,relatime,attr2,inode64,noquota
├─/run                                                    tmpfs                          tmpfs       rw,nosuid,noexec,relatime,size=3284780k,mode=755
│ ├─/run                                                  tmpfs                          tmpfs       rw,nosuid,nodev,relatime,mode=755
│ ├─/run/user/1000                                        tmpfs                          tmpfs       rw,nosuid,nodev,relatime,size=3284776k,mode=700,uid=1000,gid=1000
│ ├─/run/lock                                             tmpfs                          tmpfs       rw,nosuid,nodev,noexec,relatime,size=5120k
│ ├─/run/snapd/ns                                         tmpfs[/snapd/ns]               tmpfs       rw,nosuid,noexec,relatime,size=3284780k,mode=755
│ └─/run/netns                                            tmpfs[/netns]                  tmpfs       rw,nosuid,noexec,relatime,size=3284780k,mode=755
├─/media                                                  /dev/md2[/media]               xfs         rw,relatime,attr2,inode64,noquota
├─/mnt                                                    /dev/md2[/mnt]                 xfs         rw,relatime,attr2,inode64,noquota
└─/snap                                                   /dev/md2[/snap]                xfs         rw,relatime,attr2,inode64,noquota
  ├─/snap/core20/2015                                     /dev/loop41                    squashfs    ro,nodev,relatime
  ├─/snap/core18/2790                                     /dev/loop21                    squashfs    ro,nodev,relatime
  ├─/snap/core18/2785                                     /dev/loop37                    squashfs    ro,nodev,relatime
  ├─/snap/lxd/25086                                       /dev/loop38                    squashfs    ro,nodev,relatime
  ├─/snap/core20/1974                                     /dev/loop39                    squashfs    ro,nodev,relatime
  ├─/snap/core/15511                                      /dev/loop35                    squashfs    ro,nodev,relatime
  ├─/snap/lxd/25112                                       /dev/loop40                    squashfs    ro,nodev,relatime
  ├─/snap/core22/817                                      /dev/loop31                    squashfs    ro,nodev,relatime
  ├─/snap/core22/858                                      /dev/loop42                    squashfs    ro,nodev,relatime
  └─/snap/core/15925                                      /dev/loop36                    squashfs    ro,nodev,relatime

Ah yes so its still mounted inside the snap’s mount namespace.

Try doing:

sudo LD_LIBRARY_PATH=/snap/lxd/current/lib/:/snap/lxd/current/lib/x86_64-linux-gnu/ nsenter --mount=/run/snapd/ns/lxd.mnt -- umount /var/snap/lxd/common/lxd/storage-pools/ssd/custom/default_mmostBleveIdx

Not really… the problematic volume is mmostBleve not mmostBleveIdx (mmostBleveIdx is mmostBleve much smaller replacement)

Ah yes indeed. In that case its likely something external to LXD and the snap holding it open.