Re: [dm-devel] Snapshots

["Jun'ichi Nomura" <j-nomura ce jp nec com>]

Phillip Susi wrote:
> Jun'ichi Nomura wrote:
>> LVM2 does it by putting a linear mapping on top of the origin device.
> 
> How does this work?  I'm trying to figure out the whole locking business
> and it seems that mounting the device, or using it as a target in a dm
> table place an exclusive lock on the device, so how can you add a linear
> mapping to the origin device, if it is already used as a target in the
> snapshot device, and thus locked?

So, you have to put the linear mapping *before* that.
Then, the top-level block device will be locked but you can
still change the underlying mappings.

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation of America