> Hi James,
> 
> James Harper wrote:
> > Is it possible to mount a VSS snapshot in ntfs-3g. Eg if I have a
> > windows machine taking periodic snapshots, is it possible to mount one
> > of those instead of the 'live' filesystem?
> >
> 
> This is probably possible, and having the specifications
> surely helps. To my knowledge it has not been done yet.
> 
> > More importantly, is it possible to mount it from a running filesystem
> > via a shared block device?
> 
> An interesting question for those who would have
> already solved the first one...
> 
> In what context (remote access, virtual machine, OS
> emulation etc.) are you sharing (or wanting to share)
> a block device ?

Xen

> 
> What kind of synchronization are you suggesting to
> update the data normally kept in memory (such as
> the allocation table) ?
> 

This is probably the sticking point. I don't know if it's possible for Dom0 
(Xen host) to tell DomU (Xen guest - eg windows) to lock the snapshot and 
prevent it's deletion. I don't know either if the snapshot itself stays 
consistent at a block level - eg if a file changes is the original block 
duplicated for the snapshot or is a new block created for the updated file...

I'm not even sure if this is within the scope of ntfs-3g. Maybe it would be 
better to have a device-mapper that manages the separation of snapshots into 
devices under Linux and then ntfs-3g just sees a block device (read only, of 
course). The locking would be managed at the device-mapper level, not ntfs-3g. 
This would need a communications channel between Dom0 and DomU to handle this 
but I've done such things before...

Thanks

James


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