On Thursday, October 23, 2003, at 05:47  AM, Christian Limpach wrote:

>> Let's say you have /u1 mounted from /dev/sd1a.  How would you then 
>> take
>> a snapshot?
>
> The driver provides virtualization, so you'd use it with a userland 
> volume
> manager or with wedges and then every device you mount is provided 
> through
> the driver.  For devices mounted through the driver, you can ask the 
> driver
> to suspend access to the device (while keeping it mounted), replace the
> mapping and then resume access to the device.

Your examples aren't using a file system mounted on /dev/sd1a.  They're 
using a file system mounted on /dev/mapper/vgdelight-test.  In other 
words, you provided an example that is not what I asked for, and proved 
my point at the same time -- it requires a priori knowledge (and a 
configuration change, and use of some other software) to do snapshots 
with a pseudo-device shim.

         -- Jason R. Thorpe <thorpej@wasabisystems.com>