Thanks for the response, but I do not understand how thin-provisioning is related to question i'm asking.
As far as I understand, if 20 snapshots are created even in thin-provisioning mode, write to origin will be converted
to 21 writes. Does not it ? My scenario mean that no write multiplication occurs while making "normal" operations in
userspace (i.e. not writing to snapshots, while origin is under heavy write-load). Also, my scenario adds functionality
of "snapshot of snapshot" easily. The case I'm trying to discuss is something like chain of qcow2 files used to make
live snapshots in KVM.
Use case: having such snapshot every day. And after snapshot count exceed 30, meld first snapshot into it's origin.
This operation should be possible without any unmounting. After merging, that snapshot should contain empty diff
and so may be eliminated from chain via replacing dmsetup tables.
If someone wants to rollback - he just remove some tail of the chain + rename last item, or, create generic snapshot
from any colume in chain, or just use some point in chain. everything will work as expected.
In other words, my proposal is not connected to low-level things in LVM. Yes, all snapshots I describe can be
thin-provisioned. Just minimal logic, CLI and XML should extended.
Segmentation fault
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