[linux-lvm] LVM and chain of snapshots

Марк Коренберг socketpair at gmail.com
Wed Jan 20 12:54:05 UTC 2016

2016-01-20 17:09 GMT+05:00 Zdenek Kabelac <zkabelac at redhat.com>:

> ed sta

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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