Re: [PATCH] External device migration support

[Michael Paesold <mpaesold@gmx.at>]

Stefan Berger wrote:
> 
> "Michael Paesold" <mpaesold@gmx.at> wrote on 03/27/2006 08:31:08 AM:
> 
>  > Stefan Berger wrote:
>  >
>  > > This patch enables external devices, such as for example a mounted hard
>  > > drive image or a TPM, to be migrated to a remote machine. The patch
>  > > hooks into the checkpointing (XendCheckpoint.py) code and performs
>  > > migration in 4 different steps:
>  > ...
>  > > Please let me know what you think about this idea.
>  >
>  > I really like the idea because it seems to work for any external 
> device that
>  > can be migrated but does not allow concurrent access from both migration
>  > source and destination.
>  >
> You mean that for example concurrent access to a disk image file is not 
> possible by both systems?

I was thinking of a DRBD-backed (see http://www.drbd.org) partition that is 
replicated between two hosts (RAID-over-network). In the current version, 
this is a failover-only soluation, so only one node of a two-node cluster 
can activate the partition in r/w mode.

So if you want to migrate from host A to host B, you first have to disable 
access on host A, and only then activate access on host B. As I understood, 
this should be possible with your proposed solution. (I hope I am right)

Another use case would be a root-partition with a cow device, where you 
would have to copy the cow to the other host. If the cow is small, this 
seem reasonable, but again, it must happen after the domain is paused at 
host A and before the domain is unpaused on host B.

>  > I have not looked at the patch in detail, but I saw the specific 
> inclusion
>  > of
>  > +# The tool used for initiating virtual TPM migration
>  > +#(vtpm-migration-tool '')
>  >
>  > Could this migration tool specification be more generalized so that any
>  > device migration can be configured, not just vtpm devices?
> 
> I am going to change this and make this one single 'migration-tool'. I 
> will have that tool know by command line parameter (s.th. like '-type 
> vtpm') what device the call for migration is about. If the external tool 
> is a script you can switch over the '-type' parameter and call another 
> external program that handles that particular device type, otherwise 
> that external tool needs to know how to handle migration of all kinds of 
> devices. I will change this and repost.

Sounds good to me.

Best Regards,
Michael Paesold