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Currently I plan a migration of a large VM (MS Exchange, 300 Mailboxes and 900GB DB) from qcow2 on ext4 (RAID1) to an all-flash Ceph luminous cluster (which already holds lot's of images). The server has access to both local and cluster-storage, I only need to live migrate the storage, not machine. I have never used live migration as it can cause more issues and the VMs that are already migrated, had planned downtime. Taking the VM offline and convert/import using qemu-img would take some hours but I would like to still serve clients, even if it is slower. The VM is I/O-heavy in terms of the old storage (LSI/Adaptec with BBU). There are two HDDs bound as RAID1 which are constantly under 30% - 60% load (this goes up to 100% during reboot, updates or login prime-time). What happens when either the local compute node or the ceph cluster fails (degraded)? Or network is unavailable? Are all writes performed to both locations? Is this fail-safe? Or does the VM crash in worst case, which can lead to dirty shutdown for MS-EX DBs? The node currently has 4GB free RAM and 29GB listed as cache / available. These numbers need caution because we have "tuned" enabled which causes de-deplication on RAM and this host runs about 10 Windows VMs. During reboots or updates, RAM can get full again. Maybe I am to cautious about live-storage-migration, maybe I am not. What are your experiences or advices? Thank you very much! I was read your message two times and still can't figure out what is your question? You need move your block image from some storage to Ceph? No, you can't do this without downtime because fs consistency. You can easy migrate your filesystem via
rsync for example, with small downtime for reboot VM.
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