11:26 a.m.
Hi All,
I'm facing the problem that after adding disks to guest VM, the device
target path changed (My ovirt version is 4.3). For example:
Before adding a disk:
virsh # domblklist <vmname>
Target Source
---------------------------------------------------------
hdc -
vda /dev/mapper/3600a09803830386546244a546d494f53
vdb /dev/mapper/3600a09803830386546244a546d494f54
* vdc /dev/mapper/3600a09803830386546244a546d494f55*
vdd /dev/mapper/3600a09803830386546244a546d494f56
vde /dev/mapper/3600a09803830386546244a546d494f57
vdf /dev/mapper/3600a09803830386546244a546d494f58
After adding a disk, and then shutdown and start the VM:
virsh # domblklist <vmname>
Target Source
---------------------------------------------------------
hdc -
vda /dev/mapper/3600a09803830386546244a546d494f53
vdb /dev/mapper/3600a09803830386546244a546d494f54
*vdc /dev/mapper/3600a09803830386546244a546d494f6c*
* vdd /dev/mapper/3600a09803830386546244a546d494f55*
vde /dev/mapper/3600a09803830386546244a546d494f56
vdf /dev/mapper/3600a09803830386546244a546d494f57
vdg /dev/mapper/3600a09803830386546244a546d494f58
The devices' multipath doesn't map to the same target path as before, so in
my VM the /dev/vdc doesn't point to the old
/dev/mapper/3600a09803830386546244a546d494f55 anymore.
Anybody knows how can I make the device path mapping fixed without being
changed after adding or removing disks.
Many thanks in advance.
Joy
3:28 p.m.
New subject: Issue: Device path changed after adding disks to guest VM
On Wed, Dec 2, 2020 at 10:27 AM Joy Li <joooy.li(a)gmail.com> wrote:
Hi All,
I'm facing the problem that after adding disks to guest VM, the device target path
changed (My ovirt version is 4.3). For example:
Before adding a disk:
virsh # domblklist <vmname>
Target Source
---------------------------------------------------------
hdc -
vda /dev/mapper/3600a09803830386546244a546d494f53
vdb /dev/mapper/3600a09803830386546244a546d494f54
vdc /dev/mapper/3600a09803830386546244a546d494f55
vdd /dev/mapper/3600a09803830386546244a546d494f56
vde /dev/mapper/3600a09803830386546244a546d494f57
vdf /dev/mapper/3600a09803830386546244a546d494f58
After adding a disk, and then shutdown and start the VM:
virsh # domblklist <vmname>
Target Source
---------------------------------------------------------
hdc -
vda /dev/mapper/3600a09803830386546244a546d494f53
vdb /dev/mapper/3600a09803830386546244a546d494f54
vdc /dev/mapper/3600a09803830386546244a546d494f6c
vdd /dev/mapper/3600a09803830386546244a546d494f55
vde /dev/mapper/3600a09803830386546244a546d494f56
vdf /dev/mapper/3600a09803830386546244a546d494f57
vdg /dev/mapper/3600a09803830386546244a546d494f58
The devices' multipath doesn't map to the same target path as before, so in my VM
the /dev/vdc doesn't point to the old /dev/mapper/3600a09803830386546244a546d494f55
anymore.
Anybody knows how can I make the device path mapping fixed without being changed after
adding or removing disks.
Device nodes are not stable, and oVirt cannot guarantee that you will
get the same
node in the guest in all runs.
You should use /dev/disk/by-id/xxx links to located devices, and blkid to create
fstab mounts that do not depend on node names.
Regardless, oVirt try to keep devices stable as possible. Do you know
how to reproduce
this issue reliably?
Nir
5:57 p.m.
New subject: Issue: Device path changed after adding disks to guest VM
Thanks a lot Nir! Good to know that oVirt cannot guarantee the disk names
so that I don't need to spend more time trying to enable such a feature.
I can always reproduce the problem via my application, basically, the
procedure is as following:
1. create a VM
2. add disks to the VM (e.g.: disk names: disk1, disk3)
3. check the disk mappings via `virsh domblklist `
4. add another disk (let's say, disk2, give a name alphabetically before
some existing disks)
5. shutdown the VM via hypervisor and start it again (reboot won't work)
6. `virsh domblklist` again, then you might see the problem I mentioned
before
There are no virtio devices inside /dev/disk/by-id/xxx of my guest VM. And
I just noticed that the disks mapping information given by hypervisor (from
VM configuration or virsh command) is different from the reality inside the
VM. The disk name inside the VM was actually not changed.
So now my issue is that given a disk name (/dev/vdb) of a VM, how can I get
its wwid? Before I got it from the hypervisor, but now the hypervisor's
information is not reliable, and since the disk is unformatted, I cannot
use UUID.
Joy
On Wed, Dec 2, 2020 at 1:28 PM Nir Soffer <nsoffer(a)redhat.com> wrote:
On Wed, Dec 2, 2020 at 10:27 AM Joy Li <joooy.li(a)gmail.com>
wrote:
>
> Hi All,
>
> I'm facing the problem that after adding disks to guest VM, the device
target path changed (My ovirt version is 4.3). For example:
>
> Before adding a disk:
>
> virsh # domblklist <vmname>
> Target Source
> ---------------------------------------------------------
> hdc -
> vda /dev/mapper/3600a09803830386546244a546d494f53
> vdb /dev/mapper/3600a09803830386546244a546d494f54
> vdc /dev/mapper/3600a09803830386546244a546d494f55
> vdd /dev/mapper/3600a09803830386546244a546d494f56
> vde /dev/mapper/3600a09803830386546244a546d494f57
> vdf /dev/mapper/3600a09803830386546244a546d494f58
>
> After adding a disk, and then shutdown and start the VM:
>
> virsh # domblklist <vmname>
> Target Source
> ---------------------------------------------------------
> hdc -
> vda /dev/mapper/3600a09803830386546244a546d494f53
> vdb /dev/mapper/3600a09803830386546244a546d494f54
> vdc /dev/mapper/3600a09803830386546244a546d494f6c
> vdd /dev/mapper/3600a09803830386546244a546d494f55
> vde /dev/mapper/3600a09803830386546244a546d494f56
> vdf /dev/mapper/3600a09803830386546244a546d494f57
> vdg /dev/mapper/3600a09803830386546244a546d494f58
>
> The devices' multipath doesn't map to the same target path as before, so
in my VM the /dev/vdc doesn't point to the old
/dev/mapper/3600a09803830386546244a546d494f55 anymore.
>
> Anybody knows how can I make the device path mapping fixed without being
changed after adding or removing disks.
Device nodes are not stable, and oVirt cannot guarantee that you will
get the same
node in the guest in all runs.
You should use /dev/disk/by-id/xxx links to located devices, and blkid to
create
fstab mounts that do not depend on node names.
Regardless, oVirt try to keep devices stable as possible. Do you know
how to reproduce
this issue reliably?
Nir
6:16 p.m.
New subject: Issue: Device path changed after adding disks to guest VM
On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li(a)gmail.com> wrote:
Thanks a lot Nir! Good to know that oVirt cannot guarantee the disk names so that I
don't need to spend more time trying to enable such a feature.
I can always reproduce the problem via my application, basically, the procedure is as
following:
1. create a VM
Which guest OS? Can you share the guest disk image or ISO image used
to instal it?
2. add disks to the VM (e.g.: disk names: disk1, disk3)
3. check the disk mappings via `virsh domblklist `
Please shared the libvirt domain xml (virsh dumpxml vm-name)
4. add another disk (let's say, disk2, give a name alphabetically
before some existing disks)
Add disk while the vm is running (hotplug)?
5. shutdown the VM via hypervisor and start it again (reboot
won't work)
What do you mean by "reboot does not work?"
6. `virsh domblklist` again, then you might see the problem I
mentioned before
Mapping is different compared with state before the reboot?
There are no virtio devices inside /dev/disk/by-id/xxx of my guest
VM.
Maybe you don't have systemd-udev installed?
The links in /dev/disk/... are created by udev during startup, and
when detecting a new disk.
And I just noticed that the disks mapping information given by
hypervisor (from VM configuration or virsh command) is different from the reality inside
the VM. The disk name inside the VM was actually not changed.
So now my issue is that given a disk name (/dev/vdb) of a VM, how can I get its wwid?
Before I got it from the hypervisor, but now the hypervisor's information is not
reliable, and since the disk is unformatted, I cannot use UUID.
You can use:
# udevadm info /dev/vda
P: /devices/pci0000:00/0000:00:02.5/0000:06:00.0/virtio4/block/vda
N: vda
L: 0
S: disk/by-path/pci-0000:06:00.0
S: disk/by-id/virtio-b97e68b2-87ea-45ca-9
S: disk/by-path/virtio-pci-0000:06:00.0
E: DEVPATH=/devices/pci0000:00/0000:00:02.5/0000:06:00.0/virtio4/block/vda
E: DEVNAME=/dev/vda
E: DEVTYPE=disk
E: MAJOR=252
E: MINOR=0
E: SUBSYSTEM=block
E: USEC_INITIALIZED=10518442
E: ID_SERIAL=b97e68b2-87ea-45ca-9
E: ID_PATH=pci-0000:06:00.0
E: ID_PATH_TAG=pci-0000_06_00_0
E: DEVLINKS=/dev/disk/by-path/pci-0000:06:00.0
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9
/dev/disk/by-path/virtio-pci-0000:06:00.0
E: TAGS=:systemd:
I tried to reproduce you issue 4.4.5 development build:
Starting vm with 2 direct LUN disks:
# virsh -r dumpxml disk-mapping
...
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='3'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore type='block' index='5'>
<format type='qcow2'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
</backingStore>
<target dev='sda' bus='scsi'/>
<serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
<boot order='1'/>
<alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
<address type='drive' controller='0' bus='0'
target='0' unit='0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='2'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vda' bus='virtio'/>
<serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
<alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
<address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vdb' bus='virtio'/>
<serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
<alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
<address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
</disk>
...
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
In guest:
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
NOTE: "d9a29187-f492-4a0d-a" are the first characters of the disk id:
"d9a29187-f492-4a0d-aea2-7d5216c957d7"
seen in oVirt:
https://my-engine/ovirt-engine/webadmin/?locale=en_US#disks-general;id=d9...
Adding another disk in sorted in the middle (while the vm is running):
# virsh -r dumpxml disk-mapping
...
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='3'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore type='block' index='5'>
<format type='qcow2'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
</backingStore>
<target dev='sda' bus='scsi'/>
<serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
<boot order='1'/>
<alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
<address type='drive' controller='0' bus='0'
target='0' unit='0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='2'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vda' bus='virtio'/>
<serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
<alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
<address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vdb' bus='virtio'/>
<serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
<alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
<address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/36001405b4d0c0b7544d47438b21296ef'
index='7'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vdc' bus='virtio'/>
<serial>e801c2e4-dc2e-4c53-b17b-bf6de99f16ed</serial>
<alias name='ua-e801c2e4-dc2e-4c53-b17b-bf6de99f16ed'/>
<address type='pci' domain='0x0000' bus='0x09'
slot='0x00'
function='0x0'/>
</disk>
...
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef
In the guest:
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan 6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
Shutdown VM and start it again
# virsh -r dumpxml disk-mapping
...
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='4'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore type='block' index='6'>
<format type='qcow2'/>
<source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
</backingStore>
<target dev='sda' bus='scsi'/>
<serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
<boot order='1'/>
<alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
<address type='drive' controller='0' bus='0'
target='0' unit='0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='3'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vda' bus='virtio'/>
<serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
<alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
<address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/36001405b4d0c0b7544d47438b21296ef'
index='2'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vdb' bus='virtio'/>
<serial>e801c2e4-dc2e-4c53-b17b-bf6de99f16ed</serial>
<alias name='ua-e801c2e4-dc2e-4c53-b17b-bf6de99f16ed'/>
<address type='pci' domain='0x0000' bus='0x09'
slot='0x00'
function='0x0'/>
</disk>
<disk type='block' device='disk' snapshot='no'>
<driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
<source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
<seclabel model='dac' relabel='no'/>
</source>
<backingStore/>
<target dev='vdc' bus='virtio'/>
<serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
<alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
<address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
</disk>
...
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/36001405b4d0c0b7544d47438b21296ef
vdc /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
In the guest:
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:55
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:55
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan 6 09:55
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
Comparing to state before reboot:
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan 6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
In the guest disks are mapped to the same device name.
It looks like libivrt domblklist is not correct - vdb and vdc are switched.
Peter, this expected?
Nir
Joy
On Wed, Dec 2, 2020 at 1:28 PM Nir Soffer <nsoffer(a)redhat.com> wrote:
>
> On Wed, Dec 2, 2020 at 10:27 AM Joy Li <joooy.li(a)gmail.com> wrote:
> >
> > Hi All,
> >
> > I'm facing the problem that after adding disks to guest VM, the device
target path changed (My ovirt version is 4.3). For example:
> >
> > Before adding a disk:
> >
> > virsh # domblklist <vmname>
> > Target Source
> > ---------------------------------------------------------
> > hdc -
> > vda /dev/mapper/3600a09803830386546244a546d494f53
> > vdb /dev/mapper/3600a09803830386546244a546d494f54
> > vdc /dev/mapper/3600a09803830386546244a546d494f55
> > vdd /dev/mapper/3600a09803830386546244a546d494f56
> > vde /dev/mapper/3600a09803830386546244a546d494f57
> > vdf /dev/mapper/3600a09803830386546244a546d494f58
> >
> > After adding a disk, and then shutdown and start the VM:
> >
> > virsh # domblklist <vmname>
> > Target Source
> > ---------------------------------------------------------
> > hdc -
> > vda /dev/mapper/3600a09803830386546244a546d494f53
> > vdb /dev/mapper/3600a09803830386546244a546d494f54
> > vdc /dev/mapper/3600a09803830386546244a546d494f6c
> > vdd /dev/mapper/3600a09803830386546244a546d494f55
> > vde /dev/mapper/3600a09803830386546244a546d494f56
> > vdf /dev/mapper/3600a09803830386546244a546d494f57
> > vdg /dev/mapper/3600a09803830386546244a546d494f58
> >
> > The devices' multipath doesn't map to the same target path as before, so
in my VM the /dev/vdc doesn't point to the old
/dev/mapper/3600a09803830386546244a546d494f55 anymore.
> >
> > Anybody knows how can I make the device path mapping fixed without being changed
after adding or removing disks.
>
> Device nodes are not stable, and oVirt cannot guarantee that you will
> get the same
> node in the guest in all runs.
>
> You should use /dev/disk/by-id/xxx links to located devices, and blkid to create
> fstab mounts that do not depend on node names.
>
> Regardless, oVirt try to keep devices stable as possible. Do you know
> how to reproduce
> this issue reliably?
>
> Nir
>
6:36 p.m.
New subject: Issue: Device path changed after adding disks to guest VM
On Wed, Jan 06, 2021 at 17:16:24 +0200, Nir Soffer wrote:
On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li(a)gmail.com>
wrote:
[...]
Comparing to state before reboot:
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan 6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
In the guest disks are mapped to the same device name.
It looks like libivrt domblklist is not correct - vdb and vdc are switched.
Peter, this expected?
The names in 'virsh domblklist' are unfortunately and confusingly chosen
to match the expected /dev/ device node name, but it's at kernel's
discretion to name /dev/ nodes.
This means that it's not guaranteed that what you see in 'virsh
domblklist' will match the state in the guest.
In this case I think the reorder happens as the PCI address of vdb is
larger than the address of vdc.
A partial workaround can be to use the data provided by the qemu guest
agent, for exampe via 'virsh domfsinfo':
$ virsh domfsinfo fedora32
Mountpoint Name Type Target
------------------------------------
/ dm-0 xfs vda
/boot vda1 xfs vda
Here the guest-host matching is established via the PCI address so the
'Target' field accurately refers to the target in the VM XML.
Similarly the linux kernel recently changed enumeration of SCSI devices
so they are not guaranteed to match either. Libguestfs for example
needed a workaround.
https://github.com/libguestfs/libguestfs/commit/bca9b94fc593771b3801b09b9...
6:48 p.m.
New subject: Issue: Device path changed after adding disks to guest VM
On Wed, Jan 06, 2021 at 04:36:46PM +0100, Peter Krempa wrote:
On Wed, Jan 06, 2021 at 17:16:24 +0200, Nir Soffer wrote:
> On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li(a)gmail.com> wrote:
[...]
> Comparing to state before reboot:
>
> # virsh -r domblklist disk-mapping
> Target Source
>
---------------------------------------------------------------------------------------------------------------------------------------------------------------
> sdc -
> sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
> vda /dev/mapper/3600140594af345ed76d42058f2b1a454
> vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
> vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef
>
> # ls -lh /dev/disk/by-id/virtio-*
> lrwxrwxrwx. 1 root root 9 Jan 6 09:42
> /dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
> lrwxrwxrwx. 1 root root 9 Jan 6 09:42
> /dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
> lrwxrwxrwx. 1 root root 9 Jan 6 09:51
> /dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
>
> In the guest disks are mapped to the same device name.
>
> It looks like libivrt domblklist is not correct - vdb and vdc are switched.
> Peter, this expected?
The names in 'virsh domblklist' are unfortunately and confusingly chosen
to match the expected /dev/ device node name, but it's at kernel's
discretion to name /dev/ nodes.
This means that it's not guaranteed that what you see in 'virsh
domblklist' will match the state in the guest.
Essentially the only thing the disk device name is used for is
sorting the <disk> elements within the XML document. This in
turn affects what order PCI addresses (virtio-blk) or SCSI
LUNS (virtio-scsi) are assigned in. This influences/hints as
to what order the guest OS *might* assign device names in.
The device name from the XML is not exposed to the guest
directly though.
Certainly when hotplugging/unplugging is involved all bets are
off wrt what disk names you'll see in the guest vs the XML. Dont
expect them to match except by luck.
Regards,
Daniel
--
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5 comments
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participants (4)
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Peter Krempa