Re: [Xen-users] Migration and checkpointing

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

The -c option to xm save doesn't handle the checkpointing of storage *at all*.  
As such, you're free to use any form of storage checkpointing you want.  The 
downside is that you have to sort out the storage checkpointing you want ;-p  
As a result I'm not sure that it's actually that usable for now although the 
existence of the functionality is cool and you could certainly set up some 
interesting stuff with it.

When playing with this stuff, do be a bit careful.  It's easy to corrupt disk 
images by messing around with suspend/resume in unexpected ways.  For 
instance, if you checkpoint a domain, let it run for a bit, then destroy the 
running copy and restore the checkpoint.  The resumed domain will try and 
write to the disk, but it'll have a completely different idea of what should 
be on the disk.  This is very likely to result in damage to or loss of the 
filesystem.

Ideally, when you checkpoint the guest you'd also checkpoint the storage.  
Then if you resume the checkpoint of the guest's runtime state, you could 
first copy the backup of the storage into place.  ISTR that if you checkpoint 
a paused domain, it'll do the checkpoint and then repause the domain - at 
this point you'd be able to backup the storage and then unpause.  This would 
allow you to create a complete and consistent backup of a running domain.

Cheers,
Mark

On Monday 28 April 2008, Ian Brown wrote:
> Hello,
>   I have xen-3.1.0-13.fc8 on Fedora Core 8.
> This version supports checkpointing for "xm save" command.
>
> When running :
>
> xm save --help
>
> I get:
> Usage: xm save [-c] <Domain> <CheckpointFile>
>
> Save a domain state to restore later.
>   -c, --checkpoint   Leave domain running after creating snapshot
>
> (Though in "man xm" , --checkpoint does not show).
>
> My question is : when using --checkpoint , should I use some shared
> storage (like iSCSI)?
> Or is it not a must ? can I use LVM ? are there any restrictions on
> which storage is to be used for Xen migration with checkpointing?
> Regards,
> Ian
>
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