On Fri, Feb 17, 2017 at 12:33:28 +0100, Gionatan Danti wrote:
Hi list, I would like to understand if, and why, the --unsafe flag is needed when using --copy-storage-all when migrating guests which uses writeback cache mode.
Background: I want to live migrate guests with writeback cache from host A to host B and these hosts only have local storage (ie: no shared storage at all).
From my understanding, --unsafe should be only required when migrating writeback-enabled guests between two hosts which share non-cluster-aware storage (ie: NFS), but it should not be necessary when not sharing storage.
I think your understanding is correct.
1) it is safe to do a live migration with --copy-storage-all when guests are using writeback cache mode?
Yeah storage migration should be safe regardless of the cache mode used.
2) if so, why libvirt complains about that?
This looks like a bug in libvirt. The code doesn't check whether an affected disk is going to be migrated (--copy-storage-all) or accessed on the shared storage. Jirka