Re: [Xen-API] RE: Questions about the api

[Julian Chesterfield <julian.chesterfield@xxxxxxxxxxxxx>]

On 21/10/10 18:16, Dave Scott wrote:
> Hi,
>
>    
> > Hello everyone,
> >
> > I am writing a SR for Nexenta since I haven't found one and zfs seems
> > pretty good until now.
> > My questions are more related to missing(?) api calls.
> > I need to know if I can set the following fields in a VDI for example:
> >
> > Is-a-snapshot - there is a get_is_a_snapshot call but not a
> > set_is_a_snapshot. Same for snapshot-of. Think it's usefull just in
> > case I vdi-forget the snapshot and re introduce it with a scan or in
> > other situations.
> > parent - there is a get_parent but not a set_parent call, this would be
> > nice.
> >      
> Hm, I think there's no current way for the backend to set these VDI fields: 
> they seem to be only ever set by xapi at creation time. You're right that if 
> you forget and then re-scan then the metadata will be lost. For most backends 
> this isn't a fatal problem (although it might be annoying) but I wonder what 
> will happen for LVHD -- it uses the 'is_a_snapshot' as an indicator to decide 
> whether to 'inflate' or 'deflate' the LVM LV.
>    
That's true. Of course the issue is less critical (but still annoying) 
if LVHD provides thin provisioning. I've thought for a while that it 
would be beneficial to store more metadata persistently within the SR 
itself, to make it more portable and to overcome synchronisation issues 
like this. This was the original intention for the MGT volume in LVHD.
> We should consider allowing the backend to read/write these fields. There's 
> already precedent for that kind of thing: the backend can call 
> VDI.set_virtual_size but it looks read/only to everyone else.
>    
I would be strongly in favour of this also.

- Julian
> What do others think?
>
> Dave
>
>
>    
> > Of course I can use sm-config for example, to set a parent but still,
> > since the field is there I would like to set it myself.
> >
> > Thank you!
> > Tomoiaga Cristian
> >
> >
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> >      
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