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.
-Shawn
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