Re: [Openstack] ephemeral disks location

[Eugen Block]

Why would ephemeral instance disks be copied if the backing store is  
a shared system like Ceph.


Sorry for the confusion, I tried to describe the workflow if you use  
local disk storage for the instances. Of course there's no disk  
copying if you use a storage like ceph.



Zitat von Jay Pipes :


On 01/25/2017 03:19 AM, Eugen Block wrote:

All these instances are in our ceph cluster.

The instance path is defined in nova.conf:

# Where instances are stored on disk (string value)
instances_path = $state_path/instances

If one compute node fails but it's able to initiate a migration, the
same instance directory is created on the new host and the disks are
copied to its new compute node.


Why would ephemeral instance disks be copied if the backing store is  
a shared system like Ceph. There would be no need to copy a disk  
image since the destination host's /var/lib/nova/instances directory  
is exactly the same as the source's, right?


Best,
-jay

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Re: [Openstack] ephemeral disks location

[Jay Pipes]

On 01/25/2017 03:19 AM, Eugen Block wrote:

All these instances are in our ceph cluster.

The instance path is defined in nova.conf:

# Where instances are stored on disk (string value)
instances_path = $state_path/instances

If one compute node fails but it's able to initiate a migration, the
same instance directory is created on the new host and the disks are
copied to its new compute node.


Why would ephemeral instance disks be copied if the backing store is a 
shared system like Ceph. There would be no need to copy a disk image 
since the destination host's /var/lib/nova/instances directory is 
exactly the same as the source's, right?


Best,
-jay

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Re: [Openstack] ephemeral disks location

[Eugen Block]

Hi


where are the ephemeral disks stored?


if you decide to use local storage, your instance's disk would be stored in

---cut here---
compute1:~ # ls -l /var/lib/nova/instances/
insgesamt 60
drwxr-xr-x 2 nova nova 4096  3. Jan 11:05 14b75237-7619-481f-9636-792b64d1be17
drwxr-xr-x 2 nova nova 4096  9. Jan 14:58 284007bf-cd6b-42ee-9529-274d259e6812
drwxr-xr-x 2 nova nova 4096  9. Jan 16:13 2c408a5b-8f35-4e12-911a-36005ccff067
drwxr-xr-x 2 nova nova 4096 15. Jan 20:49 3d96bceb-4c9b-4e3c-9275-5d0bf119d47a
drwxr-xr-x 2 nova nova 4096  4. Jan 09:30 3ec7f722-12ef-4962-8059-38accf6f9a63
drwxr-xr-x 2 nova nova 4096  9. Jan 10:55 5b02c021-0b94-4d10-afc0-e0f66b492899
drwxr-xr-x 2 nova nova 4096 16. Dez 07:45 69d3e9da-2842-418c-8d62-5d2fbe805df1
drwxr-xr-x 2 nova nova 4096 19. Dez 10:13 6c30a7a8-6115-416a-820f-2bf3f9c7822f
drwxr-xr-x 2 nova nova 4096 27. Okt 15:20 911b252e-c763-4af2-a1d9-70d0880ee380
drwxr-xr-x 2 nova nova 4096 16. Jan 16:43 931f9a1e-2022-4571-909e-6c3f5f8c3ae8
drwxr-xr-x 2 nova nova 4096  4. Jan 11:19 _base
-rw-r--r-- 1 nova nova   30 25. Jan 08:33 compute_nodes
drwxr-xr-x 2 nova nova 4096 18. Jan 08:15 e96c2932-9bef-414e-bf5c-772f2c28613f
drwxr-xr-x 2 nova nova 4096 16. Dez 07:46 f87aadbf-f39d-4349-bca7-c7097e8c456e
drwxr-xr-x 2 nova nova 4096 24. Jan 13:06 locks

compute1:~ # ls -l  
/var/lib/nova/instances/14b75237-7619-481f-9636-792b64d1be17/

insgesamt 2192
-rw-rw 1 nova nova   0  3. Jan 11:05 console.log
-rw-r--r-- 1 nova nova  79  3. Jan 11:05 disk.info
-rw-r--r-- 1 nova nova 2233488  3. Jan 11:05 kernel
-rw-r--r-- 1 nova nova3259 12. Jan 12:54 libvirt.xml

compute1:~ # cat  
/var/lib/nova/instances/14b75237-7619-481f-9636-792b64d1be17/disk.info

{"/var/lib/nova/instances/14b75237-7619-481f-9636-792b64d1be17/kernel": "raw"}
---cut here---

All these instances are in our ceph cluster.

The instance path is defined in nova.conf:

# Where instances are stored on disk (string value)
instances_path = $state_path/instances

If one compute node fails but it's able to initiate a migration, the  
same instance directory is created on the new host and the disks are  
copied to its new compute node.



can I have both options?


I haven't tried it explicitly, but you can switch the option  
"images_type" in nova.conf and everytime you restart  
nova-compute.service, new instances would be created either on the  
compute nodes or in your storage (ceph) etc.
But I would not recommend that, the impact on existing instances could  
be large, e.g. if you try to resize an instance or migrate it. I don't  
think this would be a good idea. But as I said, I didn't try it  
myself, in my environment we just switched from file based instances  
to ceph. To get a better understanding how ceph works, I switched  
between file based and ceph based glance images, but only temporarily,  
of course.



Regards,
Eugen


Zitat von Manuel Sopena Ballesteros :


Hi,

I have been searching on the internet and could not find an answer  
to this question.


I understand that ephemeral disks lives until the VM is destroyed,  
but where are the ephemeral disks stored? On local host hosting the  
VM or in centralized storage (e.g. Ceph) or can I have both options?


If ephemeral can be stored on the same host the instance is  
running... what would happen if the host fails and the instance is  
migrated to another one? Will the ephemeral disk be moved across?  
Will the data persist?


Thank you very much

Manuel Sopena Ballesteros | Big data Engineer
Garvan Institute of Medical Research
The Kinghorn Cancer Centre, 370 Victoria Street, Darlinghurst, NSW 2010
T: + 61 (0)2 9355 5760 | F: +61 (0)2 9295 8507 | E:  
manuel...@garvan.org.au


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--
Eugen Block voice   : +49-40-559 51 75
NDE Netzdesign und -entwicklung AG  fax : +49-40-559 51 77
Postfach 61 03 15
D-22423 Hamburg e-mail  : ebl...@nde.ag

Vorsitzende des Aufsichtsrates: Angelika Mozdzen
  Sitz und Registergericht: Hamburg, HRB 90934
  Vorstand: Jens-U. Mozdzen
   USt-IdNr. DE 814 013 983


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[Openstack] ephemeral disks location

[Manuel Sopena Ballesteros]

Hi,

I have been searching on the internet and could not find an answer to this 
question.

I understand that ephemeral disks lives until the VM is destroyed, but where 
are the ephemeral disks stored? On local host hosting the VM or in centralized 
storage (e.g. Ceph) or can I have both options?

If ephemeral can be stored on the same host the instance is running... what 
would happen if the host fails and the instance is migrated to another one? 
Will the ephemeral disk be moved across? Will the data persist?

Thank you very much

Manuel Sopena Ballesteros | Big data Engineer
Garvan Institute of Medical Research
The Kinghorn Cancer Centre, 370 Victoria Street, Darlinghurst, NSW 2010
T: + 61 (0)2 9355 5760 | F: +61 (0)2 9295 8507 | E: 
manuel...@garvan.org.au

NOTICE
Please consider the environment before printing this email. This message and 
any attachments are intended for the addressee named and may contain legally 
privileged/confidential/copyright information. If you are not the intended 
recipient, you should not read, use, disclose, copy or distribute this 
communication. If you have received this message in error please notify us at 
once by return email and then delete both messages. We accept no liability for 
the distribution of viruses or similar in electronic communications. This 
notice should not be removed.
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