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Just for live snapshot, my understanding is the instance state will not be saved.

From: Cristian Tomoiaga [mailto:ctomoiaga at gmail.com]
Sent: Sunday, April 20, 2014 6:20 PM
To: openstack-dev at lists.openstack.org
Subject: [openstack-dev] [nova] Nova and LVM thin support

Hello everyone,

Before going any further with my implementation I would like to ask the community about the LVM thin support in Nova (not Cinder).
The current implementation of the LVM backend does not support thin LVs.
Does anyone believe it is a good idea to add support for this in Nova ? (I plan on adding support for my implementation anyway).
I would also like to know where Red Hat stands on this, since they are primarily working on LVM.
I've seen that LVM thin would be supported in RHEL 7 (?) so we may consider the thin target stable enough for production in Juno (cinder already has support for this since last year).

I know there was ongoing work to bring a common storage library implementation to oslo or nova directly (Cinder's Brick library) but I heard nothing new for some time now. Maybe John Griffith has some thoughts on this.

The reasons why support for LVM thin would be a nice addition should be well known especially to people working with LVM.

Another question is related to how Nova treats snapshots when LVM is used as a backend (I hope I didn't miss anything in the code):
Right now if we can't do a live snapshot, the instance state (memory) is being saved (libvirt virDomainManagedSave) and qemu-img is used to backup the instance disk(s). After that we resume the instance.
Can we insert code to snapshot the instance disk so we only keep the instance offline just for a memory dump and copy the disk content from the snapshot created ?

--
Regards,
Cristian Tomoiaga
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