Dm-qcow2: qcow2 as Device-mapper Block Device
Talkat ContainerCon @ Open Source Summit Europe 2022 · on Friday, 2022-09-16· at 16:50· Wicklow Hall 1 (Level 2), Convention Centre Dublin, Spencer Dock, N Wall Quay, North Wall Dublin 1, D01 T1·
summary
Describes a device-mapper driver that attaches QCOW2 images as block devices for containers, implementing request-based device-mapper path, L1/L2 table mapping, IO suspend/resume and snapshot creation via qemu-img. Supports backing files, subclusters, planned cluster compression, and a kernel-side backward merge in-kernel with forward merge handled from user space. Demonstrates why loop/NBD (vmbd) become bottlenecks at scale (quoted production scale ~500–1000 containers) and shows benchmarks and demos indicating improved density and performance.
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chapters (13)
- 0:00Intro
- 0:36Why do we need a block device?
- 2:32Ploop: in-kernel block device driver with custom image format
- 3:58qcow2 format (brief explanation)
- 4:28qcow2 format: overview
- 6:17qcow2 format features.
- 7:03Device-mapper framework
- 9:25Snapshots
- 10:20Operations with backing stores
- 11:13dm-backup
- 13:22What about qemu-nbd?
- 15:10LXC integration?
- 15:57dm-qcow2 applications: virtual machines
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