Re: [Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-25 Thread Sean Dague 
On 04/24/2016 10:15 AM, Matt Riedemann wrote:
>>
> 
> To clarify, live snapshots aren't disabled by default because they don't
> work, it's because at least with libvirt 1.2.2 and QEMU 2.0 (which is
> what we test against in the gate), we'd hit a lot of failures (about 25%
> failure rate with the devstack/tempest jobs) when running live snapshot,
> so we suspect there are concurrency issues when running live snapshot on
> a compute along with other operations at the same time (the CI jobs run
> 4 tests concurrently on a single-node devstack).
> 
> This might not be an issue on newer libvirt/QEMU, we'll see when we
> start testing with Ubuntu 16.04 nodes.

Correct. I tried to build a clarifying comment in the config option here
(as I realized it wasn't described all that well in docs) -
https://review.openstack.org/#/c/309629/

-Sean

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Re: [Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-24 Thread Matt Riedemann 

On 4/24/2016 2:09 AM, Saverio Proto wrote:

We are in an even worst situation: we have flavors with 256GB of ram
but only 100GB on the local hard disk, which means that we cannot
snapshot VMs with this flavor.

If there is any way to avoid saving the content of the ram to disk (or
maybe there is a way to snapshot the ram to, e.g., ceph), we would be
very happy.


Hello Antonio,

I received a new feedback in the Openstack patch review
(https://review.openstack.org/#/c/295865/) pointing me to this:

https://github.com/openstack/nova/blob/82a684fb1ae1dd1bd49e2a8792a2456b4d3ab037/nova/conf/workarounds.py#L72

so it looks like live snapshots are disabled because of an old buggy
libvirt. So actually this process of dumping all the RAM to disk is
not a bad design, but it is a necessary workaround because of libvirt
not being stable. It makes sense now.

At the moment I am running libvirt version 1.2.12-0ubuntu14.4~cloud0.
Maybe I can disable the workaround and try to do faster snapshots ?

Any other operator has feedback about this ?

Thank you

Saverio

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To clarify, live snapshots aren't disabled by default because they don't 
work, it's because at least with libvirt 1.2.2 and QEMU 2.0 (which is 
what we test against in the gate), we'd hit a lot of failures (about 25% 
failure rate with the devstack/tempest jobs) when running live snapshot, 
so we suspect there are concurrency issues when running live snapshot on 
a compute along with other operations at the same time (the CI jobs run 
4 tests concurrently on a single-node devstack).


This might not be an issue on newer libvirt/QEMU, we'll see when we 
start testing with Ubuntu 16.04 nodes.


--

Thanks,

Matt Riedemann


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Re: [Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-24 Thread Antonio Messina 
I actually have a card in my trello board to implement live snapshots,
pointing to this link
http://www.sebastien-han.fr/blog/2015/02/09/openstack-perform-consistent-snapshots-with-qemu-guest-agent/

However, I haven't tested it yet. If you test it let me know how it goes.

.a.

On Sun, Apr 24, 2016 at 9:09 AM, Saverio Proto  wrote:
>> We are in an even worst situation: we have flavors with 256GB of ram
>> but only 100GB on the local hard disk, which means that we cannot
>> snapshot VMs with this flavor.
>>
>> If there is any way to avoid saving the content of the ram to disk (or
>> maybe there is a way to snapshot the ram to, e.g., ceph), we would be
>> very happy.
>
> Hello Antonio,
>
> I received a new feedback in the Openstack patch review
> (https://review.openstack.org/#/c/295865/) pointing me to this:
>
> https://github.com/openstack/nova/blob/82a684fb1ae1dd1bd49e2a8792a2456b4d3ab037/nova/conf/workarounds.py#L72
>
> so it looks like live snapshots are disabled because of an old buggy
> libvirt. So actually this process of dumping all the RAM to disk is
> not a bad design, but it is a necessary workaround because of libvirt
> not being stable. It makes sense now.
>
> At the moment I am running libvirt version 1.2.12-0ubuntu14.4~cloud0.
> Maybe I can disable the workaround and try to do faster snapshots ?
>
> Any other operator has feedback about this ?
>
> Thank you
>
> Saverio



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Re: [Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-24 Thread Saverio Proto 
> We are in an even worst situation: we have flavors with 256GB of ram
> but only 100GB on the local hard disk, which means that we cannot
> snapshot VMs with this flavor.
>
> If there is any way to avoid saving the content of the ram to disk (or
> maybe there is a way to snapshot the ram to, e.g., ceph), we would be
> very happy.

Hello Antonio,

I received a new feedback in the Openstack patch review
(https://review.openstack.org/#/c/295865/) pointing me to this:

https://github.com/openstack/nova/blob/82a684fb1ae1dd1bd49e2a8792a2456b4d3ab037/nova/conf/workarounds.py#L72

so it looks like live snapshots are disabled because of an old buggy
libvirt. So actually this process of dumping all the RAM to disk is
not a bad design, but it is a necessary workaround because of libvirt
not being stable. It makes sense now.

At the moment I am running libvirt version 1.2.12-0ubuntu14.4~cloud0.
Maybe I can disable the workaround and try to do faster snapshots ?

Any other operator has feedback about this ?

Thank you

Saverio

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Re: [Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-23 Thread Antonio Messina 
We are in an even worst situation: we have flavors with 256GB of ram
but only 100GB on the local hard disk, which means that we cannot
snapshot VMs with this flavor.

If there is any way to avoid saving the content of the ram to disk (or
maybe there is a way to snapshot the ram to, e.g., ceph), we would be
very happy.

.a.

On Sat, Apr 23, 2016 at 12:31 AM, Saverio Proto  wrote:
> Hello Operators,
>
> one of the users of our cluster opened a ticket about a snapshot
> corner case. It is not possible to snapshot a instance that is booted
> from volume when the instance is paused. So I wrote this patch, and
> from the discussion you can see that I learnt a lot about snapshots.
> https://review.openstack.org/#/c/295865/
>
> Discussing about the patch I found something that I found totally
> strange, so I want to check with the community if this is the expected
> behavior.
>
> Scenario:
> Openstack Kilo
> libvirt
> rbd storage for the images
> instance booted from image
>
> Now the developers pointed to the fact that when I snapshot an active
> instance, nova makes a "managedSave"
> https://libvirt.org/html/libvirt-libvirt-domain.html#virDomainManagedSave
>
> I thought there was a misunderstanding, because I did not see the
> point of dumping the all content of the RAM to disk.
>
> I was surprised to check on the hypervisor where the instance is
> scheduled that I really see two temporary files created during the
> snapshotting process
>
> As soon as you click "snapshot" you will see this file:
>
> /var/lib/libvirt/qemu/save/instance-0001cf8c.save
>
> This file will have the size of the RAM memory of the instance. In my
> case I had to wait for 32Gb of RAM to be written to disk.
>
> Once that is finished this second process starts.
>
> qemu-img convert -O raw
> rbd:volumes/ee3a84c3-b870-4669-8847-6b9ac93a8eac_disk:id=cinder:conf=/etc/ceph/ceph.conf
> /var/lib/nova/instances/snapshots/
>
> ok this convert is also slow but already fixed in Mitaka:
> Problem description -
> http://www.sebastien-han.fr/blog/2015/10/05/openstack-nova-snapshots-on-ceph-rbd/
> Patches that should solve the problem:
> https://review.openstack.org/#/c/205282/
> https://review.openstack.org/#/c/188244/
> Merged for Mitaka -
> https://blueprints.launchpad.net/nova/+spec/rbd-instance-snapshots
>
>
> as a result you have a file with a name that looks like a uuid in this
> other folder:
>
> ls /var/lib/nova/instances/snapshots/tmpWsKqvl/
> 51574e9140204c0f89c7d86fcf741579
>
> So this means that when we take a snapshot of an active instance, we
> dump all the RAM memory into a temp file.
>
> This has an impact for us because we have flavors with 32Gb of RAM.
> Because our instances are completely rbd backed, we have small disks
> on the compute nodes.
> Also, it takes time to dump to disk 32Gb of RAM for nothing !!
>
> So, is calling managedSave the intedend behavior ? Or nova should just
> make a call to libvirt to make sure that filesystem caches are written
> to disk before snapshotting ?
>
> I tracked this call in the git, and looks like nova is implemented
> this way since 2012.
>
> Please opeators tell me that I configured something wrong and this is
> not really how snapshots are implemented :) Or explain why the dump of
> the all RAM memory is needed :)
>
> Any feedback is appreciated !!
>
> Saverio
>
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[Openstack-operators] nova snapshots should dump all RAM to hypervisor disk ?

2016-04-22 Thread Saverio Proto 
Hello Operators,

one of the users of our cluster opened a ticket about a snapshot
corner case. It is not possible to snapshot a instance that is booted
from volume when the instance is paused. So I wrote this patch, and
from the discussion you can see that I learnt a lot about snapshots.
https://review.openstack.org/#/c/295865/

Discussing about the patch I found something that I found totally
strange, so I want to check with the community if this is the expected
behavior.

Scenario:
Openstack Kilo
libvirt
rbd storage for the images
instance booted from image

Now the developers pointed to the fact that when I snapshot an active
instance, nova makes a "managedSave"
https://libvirt.org/html/libvirt-libvirt-domain.html#virDomainManagedSave

I thought there was a misunderstanding, because I did not see the
point of dumping the all content of the RAM to disk.

I was surprised to check on the hypervisor where the instance is
scheduled that I really see two temporary files created during the
snapshotting process

As soon as you click "snapshot" you will see this file:

/var/lib/libvirt/qemu/save/instance-0001cf8c.save

This file will have the size of the RAM memory of the instance. In my
case I had to wait for 32Gb of RAM to be written to disk.

Once that is finished this second process starts.

qemu-img convert -O raw
rbd:volumes/ee3a84c3-b870-4669-8847-6b9ac93a8eac_disk:id=cinder:conf=/etc/ceph/ceph.conf
/var/lib/nova/instances/snapshots/

ok this convert is also slow but already fixed in Mitaka:
Problem description -
http://www.sebastien-han.fr/blog/2015/10/05/openstack-nova-snapshots-on-ceph-rbd/
Patches that should solve the problem:
https://review.openstack.org/#/c/205282/
https://review.openstack.org/#/c/188244/
Merged for Mitaka -
https://blueprints.launchpad.net/nova/+spec/rbd-instance-snapshots


as a result you have a file with a name that looks like a uuid in this
other folder:

ls /var/lib/nova/instances/snapshots/tmpWsKqvl/
51574e9140204c0f89c7d86fcf741579

So this means that when we take a snapshot of an active instance, we
dump all the RAM memory into a temp file.

This has an impact for us because we have flavors with 32Gb of RAM.
Because our instances are completely rbd backed, we have small disks
on the compute nodes.
Also, it takes time to dump to disk 32Gb of RAM for nothing !!

So, is calling managedSave the intedend behavior ? Or nova should just
make a call to libvirt to make sure that filesystem caches are written
to disk before snapshotting ?

I tracked this call in the git, and looks like nova is implemented
this way since 2012.

Please opeators tell me that I configured something wrong and this is
not really how snapshots are implemented :) Or explain why the dump of
the all RAM memory is needed :)

Any feedback is appreciated !!

Saverio

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