[sheepdog] [PATCH v2] dog/cluster: cluster-wide snapshot save or load specified vdi

[Liu Yuan]

On Thu, Jun 05, 2014 at 11:37:19AM +0800, Ruoyu wrote:
> 
> On 2014年06月03日 20:51, Liu Yuan wrote:
> >On Tue, Jun 03, 2014 at 04:59:26PM +0800, Ruoyu wrote:
> >>It is useful for users who want to backup or restore only part of
> >>all VDIs from cluster-wide snapshot.
> >>
> >>To show which VDIs are snapshot, dog cluster snapshot show command
> >>is added.
> >>
> >>Usage and example:
> >>
> >>1. save all vdi:
> >>    dog cluster snapshot save snapname /tmp/ss
> >>
> >>2. save some specified vdi:
> >>    dog cluster snapshot save snapname /tmp/ss test0 test1 test2
> >>
> >>3. load all vdi:
> >>    dog cluster snapshot load snapname /tmp/ss
> >>
> >>4. load some specified vdi:
> >>    dog cluster snapshot load snapname /tmp/ss test6 test0 test3
> >>
> >>5. show snapshot:
> >>    dog cluster snapshot show snapname /tmp/ss
> >I've tried the following command
> >
> >yliu at ubuntu-precise:~/sheepdog$ dog/dog vdi list
> >   Name        Id    Size    Used  Shared    Creation time   VDI id  Copies  Tag
> >s test         1  100 MB   12 MB  0.0 MB 2014-06-03 20:43   7c2b25      2            s1
> >s test         2  100 MB  4.0 MB  8.0 MB 2014-06-03 20:43   7c2b26      2            s2
> >s test         3  100 MB  4.0 MB  8.0 MB 2014-06-03 20:43   7c2b27      2            s3
> >   test         0  100 MB  0.0 MB   12 MB 2014-06-03 20:44   7c2b28      2
> >yliu at ubuntu-precise:~/sheepdog$ dog/dog cluster snapshot list ./snap
> >Index		Tag		Snapshot Time
> >1		test		Tue Jun  3 20:45:05 2014
> >yliu at ubuntu-precise:~/sheepdog$ dog/dog cluster snapshot show test ./snap
> >The cluster-wide snapshot contains these VDIs:
> >hello
> >
> >
> >
> >world
> >
> >brazil
> >
> >test
> >test
> >test
> >
> >yliu at ubuntu-precise:~/sheepdog$ dog/dog cluster snapshot save test2 ./snap s1 s2
> >Object not found. It may be caused by:
> >1. The specified VDIs are not found.
> >2. The specified VDIs don't have snapshots.
> >Fail to save snapshot to path: ./snap.
> >
> >-----
> >
> >'show' doesn't work as expected. And seems that this patch can't save specified
> >snapshots. In above example, I want to save snapshots with the tag name 's1' and
> >'s2' of the test tree.
> >
> >Of you are intended to save just tip snapshots of specified snapshot name?
> >
> >I'd suggest following
> >
> >dog cluster snapshot save test2 ./snap test:s1 test:s2
> >
> >command to save specified snapshots.
> I think I did not understand cluster snapshot correctly. I will
> update it later.
> But, I suggest the cluster wide snapshot should be based on
> specified VDIs, not be based on its' snapshots.
> Otherwise, some elements of the restored VDI object, such as vdi_id
> and parent_vdi_id, may be different to the original one if we choose
> part of the snapshots of the VDI.
> 

I suggest we use vdi name to represent a whole chain of snapshots. For example,

test(base)->snap1->snap2->snap3
       |
       +---->snap4->working vdi named test

when we specify test as parameter for 'cluster snapshot save' we should store
the whole chain, namely test(base), snap{1,2,3,4}.

so does for 'load' command.

Thanks
Yuan