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public:trouble:dm [2016/02/10 20:01] – [Solution] fixed footer links wiki.tkpublic:trouble:dm [2017/11/12 03:08] (current) – [Solution] Updated link wiki.tk
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 +===== Remaining DM devices =====
 +==== Error description ====
 +LVM devices are often generated and removed by automatic processes. Examples are the creation of vhosts or the generation of snapshots while performing backups. During these processes LVM devices are sometimes removed while belonging DM devices still remain. The error becomes visible when LVM partitions cannot be created. This happens because DM devices of the same name still exist.
 +  root@kvm55:~# lvs
 +    LV              VG           Attr   LSize   Origin …
 +    images          vg           -wi-ao 200.00g
 +    lv_dbslave5501  vg           -wi-a-  20.00g
 +    lv_dbserver5501 vg3_dbserver -wi-ao   4.98g
 +    lv_nas5501      vg3_nas      -wi-ao 499.98g
 +  
 +  root@kvm55:~# dmsetup ls
 +  vg-images                    (252:0)
 +  vg-lv_dbslave5501            (252:1)
 +  350002ac21d632071            (252:2)
 +  vg3_dbserver-lv_dbserver5501 (252:3)
 +  350002ac21d622071            (252:4)
 +  vg3_nas-lv_nas5501           (252:5)
 +  vg3_nas-lv_nas5501_snapshot  (252:6)
 +In the depicted example above the command ''lvs'' displays no snapshot for the LVM partition 'lv_nas5501'. But the belonging dm device 'vg3_nas-lv_nas5501_snapshot' still exists as the output of the command ''dmsetup'' shows. In this case the creation of a snapshot with the same name will fail:
 +  root@kvm55:~# lvcreate -s -n lv_nas5501_snapshot -L 5G \
 +  /dev/vg3_nas/ lv_nas550
 +    Locical volume “lv_nas5501_snapshot“ already exists in volume group “ vg3_nas“
 +==== Failure cause ====
 +The failure cause is completely unknown. Because automatic processes often lead to the error, it is hard to observe the error cause.
 +==== Solution ====
 +It is possible to remove the DM device directly. Before removal check, whether the DM device still has open connections:
 +  root@kvm55:~# dmsetup info /dev/dm-6
 +  Name:              vg3_nas-lv_nas5501_snapshot
 +  State:             ACTIVE
 +  Read Ahead:        256
 +  Tables present:    LIVE
 +  Open count:        0
 +  Event number:      1
 +  Major, minor:      252, 6
 +  Number of targets: 1
 +  UUID: LVM-keMgdvei4HyiAJrdMgW8EEa8Q8vTze6cVsvVBap2GKZ5oqeO6KBNOUEZTBw8
 +In the example above the device has no open connections (Open count: 0) and can be removed:
 +  root@kvm55:~# dmsetup remove /dev/dm-6
  
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