date:20130703

Re: [openstack-dev] [cinder] Propose to add copying the reference images when creating a volume

2013-07-03 Thread Sheng Bo Hou

Hi Vish,

I would like you to review this patch
https://review.openstack.org/#/c/35460/.

I think this approach takes the least effort to fix this issue.
When we boot an instance from a volume, nova can get the volume
information by _get_volume. kerel_id and ramdisk_id are already in the
volume information. We just need to make nova retrieve them. In the code
of creating instance, kernel_id and ramdisk_id are accessed by checking
"properties"(many parts), but the volume information saved them in
"volume_image_metadata". I just convert the data structure a bit and save
two of this params in "properties", and it can work.

Well, if you do not see it favorable, we can work it out in another way.

Thank you.

Best wishes,
Vincent Hou (侯胜博)

Staff Software Engineer, Open Standards and Open Source Team, Emerging
Technology Institute, IBM China Software Development Lab

Tel: 86-10-82450778 Fax: 86-10-82453660
Notes ID: Sheng Bo Hou/China/IBM@IBMCNE-mail: sb...@cn.ibm.com
Address:3F Ring, Building 28 Zhongguancun Software Park, 8 Dongbeiwang
West Road, Haidian District, Beijing, P.R.C.100193
地址:北京市海淀区东北旺西路8号中关村软件园28号楼环宇大厦3层 邮编：100193

Vishvananda Ishaya
2013/07/02 01:14
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jsbry...@us.ibm.com, "Duncan Thomas John
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Re: [openstack-dev] [cinder] Propose to add copying the reference images
when creating a volume

On Jul 1, 2013, at 3:35 AM, Sheng Bo Hou wrote:

Hi Mate,

First, thanks for answering.
I was trying to find the way to prepare the bootable volume.
Take the default image downloaded by devstack, there are three images:
cirros-0.3.0-x86_64-uec, cirros-0.3.0-x86_64-uec-kernel and
cirros-0.3.0-x86_64-uec-ramdisk.
cirros-0.3.0-x86_64-uec-kernel is referred as the kernel image and
cirros-0.3.0-x86_64-uec-ramdisk is referred as the ramdisk image.

Issue: If only the image(cirros-0.3.0-x86_64-uec) is copied to the volume
when creating a volume) from an image, this volume is unable to boot an
instance without the references to the kernel and the ramdisk images. The
current cinder only copies the image cirros-0.3.0-x86_64-uec to one
targeted volume(Vol-1), which is marked as bootable but unable to do a
successful boot with the current nova code, even if image-id is removed in
the parameter.

Possible solutions: There are two ways in my mind to resolve it. One is we
just need the code change in Nova to let it find the reference images for
the bootable volume(Vol-1) and there is no need to change anything in
cinder, since the kernel and ramdisk id are saved in the
volume_glance_metadata, where the references point to the images(kernel
and ramdisk) for the volume(Vol-1).

You should be able to create an image in glance that references the volume
in block device mapping but also has a kernel_id and ramdisk_id parameter
so it can boot properly. I know this is kind of an odd way to do things,
but this seems like an edge case and I think it is a valid workaround.

Vish

The other is that if we need multiple images to boot an instance, we need
a new way to create the bootable volume. For example, we can create three
separate volumes for three of the images and set the new references in
volume_glance_metadata with the kernel_volume_id and ramdisk_volume_id.
The benefit of this approach is that the volume can live independent of
the existence of the original images. Even the images get lost
accidentally, the volumes are still sufficient to boot an instance,
because all the information have been copied to Cinder part.

I am trying to looking for the "another way to prepare your bootable
volume" as you mentioned and asking for the suggestions.
And I think the second approach could be one way. Do you think it is a
good approach?

Best wishes,
Vincent Hou (侯胜博)

Staff Software Engineer, Open Standards and Open Source Team, Emerging
Technology Institute, IBM China Software Development Lab

Mate Lakat
2013/07/01 04:18

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Re: [openstack-dev] [cinder] Propose to add copying the reference images
when creating a volume

Hi,

I just proposed a patch for the boot_from_volume_exercise.sh to get rid
of --image. To be honest, I did not look at the various execution paths.
My initial thought is that boot from volume means you boot from volume.
If you only have a kernel + ramdisk image, I simply assumed that you
can't do it.

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