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I have several multipath iSCSI LUN's formatted as ocfs2 filesystems. They are part of an Ubuntu 14.04 cluster using local heartbeat. This all appears to be working fine if I mount them manually after rebooting.

If I try to automatically mount them by UUID via fstab (even with _netdev option) I run into issues.

If I have fstab entries (such as the following) commented out during a boot

UUID=094c02f6-bfbb-4fe5-8a90-3b6992c81a60     /mnt/lun-1   ocfs2   _netdev        0       0

and then uncomment them once logged in and run mount -a everything seems fine. i.e. multipath -ll shows multiple paths to each iSCSI device. e.g.:

3603be8bfce91e3e06e63e5ad426f4d98 dm-5 EQLOGIC ,100E-00
size=15T features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  |- 19:0:0:0 sdr 65:16 active ready  running
  `- 20:0:0:0 sdf 8:80  active ready  running

and mount shows that /dev/mapper/* devices for my iSCSI LUN's:

/dev/mapper/3603be8bfce91e3e06e63e5ad426f4d98-part1 on /mnt/lun-1 type ocfs2 (rw,_netdev,heartbeat=local)

However, if I then reboot with the same fstab entry uncommented, I don't get the same multipath -ll output. Namely, only a single multipath device is present, not one for each iSCSI LUN.

mount shows the device not as /dev/mapper/* but to just a single non-multipath'd device like /dev/sdc1.:

/dev/sdk1 on /mnt/lun-1 type ocfs2 (rw,_netdev,heartbeat=local)

Am I doing something wrong, or is this caused by multipath not being fully up-and-running before my ocfs2 multipath devices are mounted?

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3 Answers 3

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The problem seems to be as I expected, either multipath isn't up fully or open-iscsi hasn't yet logged into iscsi targets for all paths when the ocfs2 fstab entries are mounted. This is despite having _netdev as a mount option.

I tried messing around with init.d scripts for /etc/init.d/o2cb and /etc/init.d/ocfs2 by adding iscsi and multipath-tools to their Should-Start: and Should-Stop: lines. But couldn't seem to get this ocfs2 multipath mounting by UUID to work properly.

If I instead use the relevant multipath device (e.g. /dev/mapper/3603be8bfce91e3e06e63e5ad426f4d98-part1) rather than the UUID things boot normally and the mount via fstab works correctly using multipath.

The reason I didn't try this initially was that I wanted something to work across multiple hosts which may or may not have multipath. So in the end I have different devices depending on whether I'm on a host with or without multipath. This isn't ideal, but seems to be working.

fstab on Host with Multipath

/dev/mapper/3603be8bfce91e3e06e63e5ad426f4d98-part1 /mnt/lun-1 ocfs2 _netdev 0 0

fstab on Host without Multipath

/dev/disk/by-id/scsi-3603be8bfce91e3e06e63e5ad426f4d98-part1 /mnt/lun-1 ocfs2 _netdev 0 0
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I had a very similar problem recently and found this bug:

https://bugs.launchpad.net/ubuntu/+source/multipath-tools/+bug/1547206

So far the work-around of installing the older version and holding it at that version seems to be working. It seems to have resolved all the boot hanging and ordering issues I was having with the current version of the package.

apt-get install multipath-tools=0.4.9-3ubuntu7

apt-mark hold multipath-tools

aptitude hold multipath-tools

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I've had a similar problem when trying to mount physical disks in a JBOD that are reachable via two paths. A race between multipath device creation and mounting drives by filesystem UUID happens on every boot. Some devices are mounted using the single path, whereas others use the correct multipath device.

Looking at /etc/multipath/bindings I can see that there is a static mapping between the WWID (globally unique drive serial number) and the mpath{a-z} devices. Using filesystem UUIDs to work around non-persistent drive letters was simply not necessary since multipathd implements its own persistent mapping that ensures drive letters do not change across reboots or changes in physical drive attachment.

I cannot say whether this solution applies to iSCSI, but it did work for me for physical multipath devices.

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