Background snapshot

Explore the concept of background snapshot in virtual machine management, including details on VM snapshot types, workflow, user experience, and current status. Learn about storing VM states, disk snapshots, memory access tracking, and more.

• Virtual machines
• Snapshot management
• VM state
• Background snapshot
• Memory tracking

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Presentation Transcript

1. Background snapshot by Denis Plotnikov KVM Forum October 24 26, 2018

2. Agenda Snapshot overview 01 Background snapshot details 02 How to use 03 2

3. What is Background snapshot? 01 The way to store a complete VM state with minimal downtime 02 03 3

4. What is VM snapshot? 01 Disk state (disk snapshot) 02 + Other VM devices' states 03 vCPUs, RAM, controllers, etc. 4

5. What are the VM snapshot types? Depends on where vm devices state is stored: 01 Internal External 02 The state is stored inside the disk The state is saved on fs, net, etc. VS Format driver support is needed: qcow2 03 5

6. Background snapshot details 01 02 HARDEST PART: VM memory access tracking 03 Uses migration code Copy memory page 6

7. VM memory access tracking 01 mprotect sigsegv catch userfaultfd WP-mode isn't a part of mainsream linux 02 Too many places to track access 03 7

8. Background snapshot workflow Enable background snapshot: (qemu) migrate_set_capability background-snapshot on 01 Make a disk snapshot Wait until done (qemu) snapshot_blkdev <disk_name> <path> 02 RAM saving 03 Pause VM Start VM state saving (qemu) stop (qemu) migrate <type:destination> 8

9. User experience 01 VM slows down while snapshotting depending on the load 02 03 Downtime from 20 less than 1 sec 9

10. Current status 01 02 Waiting for userfaultfd-wp landing to mainstream linux 03 Draft implementation 10

11. QUESTIONS? 11

12. Thanks!