What if the BDM Layout is versioned ?

If the BDM (Block, Digest, Metadata) layout is versioned, it introduces an additional layer of complexity but significantly enhances the ability to track, retrieve, and reconstruct files or chunks across multiple versions. Here’s how the algorithm and system adapt to handle versioning effectively:

Versioned BDM Layout Overview

Block (B):

Data chunks remain immutable.

Deduplication ensures that unchanged chunks between versions are reused.

Digest (D):

Hashes uniquely identify chunks.

Versions of a file use the same digest for identical chunks, avoiding redundancy.

Metadata (M):

Stores the list of chunk hashes, order, sizes, and additional versioning information, such as:

Version ID or timestamp.

Parent-child relationships between versions.

Change deltas (e.g., added/removed chunks).

Algorithm for Versioned Chunk Retrieval

Steps:

Step 1: Locate Metadata for the Version

Step 2: Determine Chunk Changes

Step 3: Retrieve Chunk Data

Step 4: Reconstruct the File

Handling Advanced Scenarios

Version Map

The metadata for a versioned BDM layout typically includes a version map or a hierarchical structure (e.g., Merkle tree, DAG) that links:

Parent and child versions.

Changed chunks (deltas) between versions.

Optimized Retrieval

Avoid redundant fetching:

Chunks unchanged across versions are fetched once and reused.

Use references or symbolic links to avoid duplicating chunks in metadata.

Storage Efficiency

Immutable chunks: Deduplicated storage ensures that even if a file has multiple versions, identical chunks are stored once.

Delta storage: Only store and fetch the changes (added or modified chunks) for newer versions.

Example Walkthrough

Advantages of Versioned BDM Layout

Efficiency:

Deduplicated chunks save storage and retrieval time.

Metadata tracks changes incrementally.

Versioning:

Deltas allow efficient reconstruction of any version.

History tracking enables point-in-time recovery

Scalability:

Supports large datasets and frequent version updates.

Flexibility:

Can reconstruct files at any granularity (chunk or full version).