[pve-devel] [PATCH 1/3] add live storage migration with vm migration

[Alexandre DERUMIER]

>>setting new drive in pending until the whole migration is done, so user can use revert ?
>>I think it should done manually by user, because maybe user don't want to loose new datas written to target storage.


Another possibility : create a new vmid on target host, with his own config. 
Like this user can manage old and new vm after migration . and If something crash during the migration,this is more easier.

The only drawback is that we can't mix local && shared storage in this case. (but I think that if user have shared storage, he don't have need of local storage migration)



----- Mail original -----
De: "aderumier" <aderumier at odiso.com>
À: "Wolfgang Bumiller" <w.bumiller at proxmox.com>
Cc: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Lundi 17 Octobre 2016 15:52:14
Objet: Re: [pve-devel] [PATCH 1/3] add live storage migration with vm migration

>>So we'd need a way to switch back, then again the remote side might be 
>>dead at this point... we could try though? 

setting new drive in pending until the whole migration is done, so user can use revert ? 
I think it should done manually by user, because maybe user don't want to loose new datas written to target storage. 


About multiple disks, I thinked that we can't use transactions, 
but reading the livirt mailing it seem possible to launch multiple drive-mirror in parallel 
https://www.redhat.com/archives/libvir-list/2015-April/msg00727.html 



----- Mail original ----- 
De: "Wolfgang Bumiller" <w.bumiller at proxmox.com> 
À: "aderumier" <aderumier at odiso.com> 
Cc: "pve-devel" <pve-devel at pve.proxmox.com> 
Envoyé: Lundi 17 Octobre 2016 15:41:49 
Objet: Re: [pve-devel] [PATCH 1/3] add live storage migration with vm migration 

On Mon, Oct 17, 2016 at 03:33:38PM +0200, Alexandre DERUMIER wrote: 
> >>considering some of the code looks like it's prepared for multiple 
> >>disks, I wonder if the remote side should send a mapping containing the 
> >>old + new names? 
> 
> yes, I think it can prepare output for multiple disks, it'll be easier later. 
> Maybe simply send multiple lines, 1 by disk ? 
> 
> 
> 
> > + PVE::QemuServer::qemu_drive_mirror($vmid, $self->{target_drive}, $nbd_uri, $vmid); 
> > + #update config 
> 
> >>As far as I can see you have qemu running on the remote side already, 
> >>since you use hmp/mon commnads to export the nbd devices, so it seems 
> >>it would be a better choice to update this after the migration has 
> >>completed, and change the cleanup code below to detach the nbd drive. 
> 
> The problem is that when drive_mirror is finished, the source vm write to the remote disk. 

So we'd need a way to switch back, then again the remote side might be 
dead at this point... we could try though? 

> So I think it's better to update config, to have the new disk in config. 
> If source host die before end of livemigration, user only need to move the config file to destination host. 
> 
> 
> Alternativly, I was thinking to use pending to store new local disk path, and switch at the end of the live migration. 
> Maybe add a node=xxx option to drive during the migration, to known where the local disk is located exactly. 
> I'm not sure... 

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