Bug#799781: device lock race condition between udev and multipathd may cause systemd to abort system boot

[Ritesh Raj Sarraf]

On Mon, 2015-10-05 at 14:30 +0000, Baumgartner Niels, Bedag wrote:
> Hi Ritesh
> 
> > then you can mount the filesystem like this:
> >   mount /dev/mapper/36000393000007d3901000000fef00a2d /mnt or this
> >   mount /dev/disk/by-id/scsi-36000393000007d3901000000fef00a2d /mnt
> > You should prefer the latter, as this will work whether or not
> > multipath-tools is installed.
> 
> Ok, my /etc/fstab uses the /dev/mapper/<id> instead of /dev/disk/by-
> id/scsi-<id> 
> 
> /dev/mapper/vg_system-lv_system /       ext4    errors=remount-
> ro       0       1
> # /boot was on /dev/sdb1 during installation
> /dev/mapper/360060e80165082000001508200009083-
> part1     /boot   ext4    defaults        0       2
> # swap was on /dev/sdb2 during installation
> /dev/mapper/360060e80165082000001508200009083-
> part2     none    swap    sw      0       0
> 

It is not that simple. :-)

Both LVM and Multipath are targets of Device Mapper framework. So in
both cases, you see the maps in /dev/mapper/


Your drive is a partitioned drive, something we don't recommend when
using multipath devices. I'm assuming the missing sda3 partition is the
one on top of which the LVM set is created.

> > Now, in a setup, if you mix Device Mapper LVM and Device Mapper
> > Multipath, you need to ensure that the multipath map is created
> > before LVM locks it.
> 
> How would I do this?
> 

I don't work on storage currently, so my instructions may not be
correct.

You need to create PVs on top of multipath devices. So, in your case,
it may make sense to blacklist /dev/sd* in lvm.conf.

And in multipath, make sure that your maps are created, and all paths
are listed. These days, mutlipath by default, blackslists everything.
So create a multpath.conf file that suits your setup.


> > And to LVM, you need to instruct that it should look for Physical
> > Volumes in /dev/mapper/.
> The following line is present from the default lvm.conf:
>     scan = [ "/dev" ]
> 

I'm not sure of the specifics. Please check online, and try
possibilities. You need to ensure what I mentioned above.

> So here is what I could try:
> 1. install stable packages
> 2. change /etc/fstab to use /dev/disk/by-id devices.
> 3. change lvm.conf to 
>   scan = ["/dev/disk/by-id/"]
> 4. update-initramfs
> 5. test again
> 

No. If you use LVM setup, then you still need to add a /dev/mapper/vg-
lv entry in /etc/fstab

Same applies for multipath too.

One uses /dev/disk/by-*/ references for persistent SCSI device names
only.


> This way the scsi devices should not be locked by lvm.
> Might this work? Is there anything else I should do/change before
> testing again?
> 

I'd suggest you start with reading the wonderful Storage Administration
Guide by Red Hat.

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/
6/html-single/Storage_Administration_Guide/

This will give you answers to most of your questions, and then you can
relate it to Debian.


-- 
Ritesh Raj Sarraf
RESEARCHUT - http://www.researchut.com
"Necessity is the mother of invention."

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