[dm-devel] new multipath device mistakenly replaced another PV in existing volume group

[Benjamin Marzinski]

On Wed, Apr 19, 2017 at 02:58:47PM -0700, Neutron Sharc wrote:
> I'm seeing a strange problem (iscsi LUNs + dm-multipath + lvm) that I
> will walk through an example to explain.
> 
> I have an iscsi target machine that exposes many iscsi LUNs. Iscsi
> initiator logs in 4 iscsi LUNs (vol1_[0-3]),  creates a multipath
> device for each LUN (/dev/mapper/vol1_[0-3]), and combines the 4
> multipath devices into a volume group and LV (vol1/vol1_lv).
> 
> Then I log in another 4 iscsi LUNs (vol3_[0-3]), create a multipath
> device for each new LUN (/dev/mapper/vol3_[0-3]).  Now there is a
> strange thing:
> some new multipath devices (/dev/mapper/vol3_0, /dev/mapper/vol3_2 in
> this example) replaced existing PVs in vol1.  As a result, these new
> multipath devices have open-count > 0, so I cannot pvcreate on them:
> 
> $ sudo dmsetup ls --tree
> vol1-vol1_lv (252:4)
>  ├─vol3_0 (252:9)   <==  fresh multipath device, should NOT be in vol1
>  │  └─ (65:128)
>  ├─vol3_2 (252:10)  <==  fresh multipath device, should NOT be in vol1
>  │  └─ (65:144)
>  ├─vol1_1 (252:1)
>  │  └─ (65:48)
>  └─vol1_0 (252:0)
>     └─ (65:32)
> vol1_3 (252:3)  <== was in vol1-vol1_lv, but knocked out
>  └─ (65:16)
> vol1_2 (252:2)  <== was in vol1-vol1_lv, but knocked out
>  └─ (65:64)
> vol3_3 (252:11)
>  └─ (65:160)
> vol3_1 (252:12)
>  └─ (65:176)
> 
> 
> Please note that all these vol3_[0-3] are fresh, without any LVM
> metadata on them, as shown by pvscan::
> 
> sudo pvscan --cache /dev/mapper/vol3_0
>   Incorrect metadata area header checksum on /dev/mapper/vol3_0 at offset 4096
>   Incorrect metadata area header checksum on /dev/mapper/vol3_0 at offset 4096
>   Incorrect metadata area header checksum on /dev/mapper/vol3_0 at offset 4096
> 
> 
> $ sudo pvcreate /dev/mapper/vol3_0   <== this multipath device was
> mistakenly included into vol1
> 
>   Found duplicate PV 9F6vU9NVBfEq1w3e04T5UreO6fDVPJNy: using
> /dev/mapper/vol1_3 not /dev/mapper/vol3_0
>   Using duplicate PV /dev/mapper/vol1_3 without holders, replacing
> /dev/mapper/vol3_0
>   Can't open /dev/mapper/vol3_0 exclusively.  Mounted filesystem?
> 
> 
> ========== Configs I used:
> BTW,  I have enabled lvmetad,  my lvm.conf has this:
> filter = [ "a|/dev/mapper/.*|", "r|.*|" ]
> global_filter = [ "a|/dev/mapper/.*|", "r|.*|" ]
> 
> My /etc/multipath.conf is:
> defaults {
>   user_friendly_names     yes
>   path_grouping_policy    failover
>   polling_interval        10
>   path_selector           "round-robin 0"
>   find_multipaths         yes
>   features       "1 queue_if_no_path"
> }
> blacklist {
>   devnode  "^sda[1-9]"
> }
> multipaths {
>   multipath {
>     wwid 360000000758757de9fb289cbde12abab
>     alias vol1_0
>   }
>   // more devices
> }
> 
> iscsi initiator is on centos 6.5, with pkgs version:
> lvm2-2.02.143-12.el6.x86_64
> device-mapper-multipath-0.4.9-100.el6.x86_64
> 
> iscsi target is tgtd on another Ubuntu machine.
> 
> 
> 
> Comments are appreciated.

Have you tried this with multipathing removed? Does the same thing still
happen? multipath shouldn't be changing your LVs. The reassign_maps code
(which could do that) isn't in RHEL6. Does this work correctly with
lvmetad turned off?

-Ben

> 
> 
> -Shawn
> 
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