[dm-devel] Recommendations for cascaded snapshots

[Alasdair G Kergon]

On Sun, Oct 01, 2006 at 03:12:01PM -0400, Kyle Moffett wrote:
> Another quickie question:  How can I measure the current %use of a  
> given snapshot device?  

lvs -o snap_percent vgname/lvname
(see man page for formatting options to control output units & suppress
headings etc.)

> My first "solution" was to use stacked snapshots such that the  

See the list archives for the thread last week.
I'll review the concept & initial code later this week.
[see LVM2/lib/report/columns.h in the source tree for the definitive 
list of fields; we should probably fix the tools to display the
list that got compiled in.]

> First of all, it doesn't seem  
> possible to merge two snapshots together

Mark has code to do this for read-only origins (originally implemented in
userspace).

> but I couldn't determine how stable it was or whether  
> or not it applied to recent kernels.

I'm part-way through integrating it.
Once the snapshot concurrent read/write bug fix is finally sorted out, it
shouldn't take long.
 
Alasdair
-- 
agk at redhat.com