Snapshots TODO

Table of Contents Bugs Features Testing Benchmarks

Bugs

• Directory rename across multiple snapshots
• CoW files that are open during snapshot take
• CoW files that are mmaped during snapshot take
• Check if file was CoW after read/get operation to validate the result

Features

• Script for simple overlayfs snapshot management (mount, create, delete)
• Take a new snapshot without un-mounting the writable mount

  mount -t overlay snapN -o lowerdir=/lower,upperdir=/upper/N,workdir=/work /snap/N
  mount -o remount,snapshot=/snap/N /mnt

• Freeze snapshot mount before snapshot take (remount)
• Take a new snapshot without un-mounting older snapshot mounts

  mount -o remount,lowerdir=/upper/0:.../upper/N-1:/snap/N /snap/0

• Snapshot offline delete - merge of un-mounted overlayfs layers
  • Merge 2 layers and cleanup whiteouts that do not cover anything
• Snapshot online delete - merge of mounted overlayfs layers
  • "Move up" from lower to upper and delete remaining lower files
• Overlayfs snapshots support for snapper

Testing

• Run stress tests with concurrent file system operations on writable mount to prove race free and low locks contention overhead
• Run stress tests with concurrent access to the same file/dir in writable mount and in read-only snapshot to prove race free and low locks contention overhead

Benchmarks

• Run performance benchmarks on writable mount to prove low overhead
• Run performance benchmarks on read-only snapshots to measure the performance overhead compared to local file system access