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Re: [lvm-devel] [PATCH] Enable (already implemented?) snapshots of mirrors




On Oct 21, 2009, at 8:08 AM, Alasdair G Kergon wrote:

On Thu, Oct 15, 2009 at 03:19:08PM -0500, Jon Brassow wrote:
I just wanted to get a feel for where things were at WRT snapshots of
mirrors.  Pulling out the prevention check (patch provided below),
things seem to work just fine.  Is there something I am missing?

Well the check was inserted because the code was untested.

All the newly-possible combinations of commands need to be tested before
it can be removed, and other 'unsupported' messages can be placed
where things don't work correctly.

(Basically you check through all the options of all the commands
one-by-one and test every aspect which might behave differently
in respect of snapshots of mirrors. This includes checking the dmeventd
plugins as well as 'partial' VGs, and ensuring there are no ways of
manipulating the 'in-use' mirror that conflict with the fact it is
an origin, and ensuring display tools remain comprehensible.)

Ok, I'll get things started.  You can tell me if I miss anything.(?)

lvcreate:
+ snapshot of mirror

lvresize:
+ grow the mirror origin (but only if inactive)
+ grow the snapshot exception store
+ Warning message given when trying to shrink origin
+ able to shrink exception store (warning is given and asks to proceed)

lvchange:
+ '-an <origin>' deactivates origin and all snapshots
+ '-ay <origin>' activates origin and all snapshots

lvconvert:
+ Error message notifying you cannot convert an LV under a snapshot (this could be removed?)

dmeventd:
- since you can't convert an lv under a snapshot, you cannot repair a mirror when a device fails

So far, it seems like the 'dmeventd' issue must be fixed before a possible check-in.

 brassow


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