Storage Space Savings Reporting Using Dense Tree Counters
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Solution Overview
Problem
Storage systems face challenges in accurately reporting storage space savings for snapshots and clones due to the skewing effect of reference counts from copy-on-write operations, which can inflate storage space consumption in de-duplicated and compressed environments.
Innovation Solution
The implementation of multi-level dense tree metadata structures and space adjustment counters, such as the clone space adjustment (CSA) and diverged space adjustment (DSA) counters, allows for accurate calculation and reporting of storage space savings by accounting for shared and diverged data across volumes, ensuring precise deduplication savings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If reference counting is used for de-duplication in snapshots and clones, then storage space efficiency is improved, but measurement precision of space savings deteriorates due to skewing from copy-on-write operations
Solution Approach 1:
The patent segments the storage space calculation into two distinct components: logical space (total space allocated to volumes) and physical space (actual space consumed on storage devices). By separating these measurements and tracking them independently through reference counting mechanisms, the system can report accurate space savings that reflect actual physical consumption rather than being skewed by logical reference counts from copy-on-write operations.
2Reliability
If copy-on-write operations are performed for snapshots and clones, then data integrity and versioning are improved, but storage space consumption increases due to metadata duplication
Solution Approach 1:
The patent implements preliminary action by pre-allocating space adjustment counters (such as CSA and DSA counters) during snapshot and clone creation, before actual copy-on-write operations occur. These counters are initialized to track the space consumed by metadata structures, allowing the system to anticipate and account for future space consumption from COW operations rather than reacting to it afterward. This enables accurate space reporting while maintaining data integrity through proper COW implementation.
3Quantity of substance
If de-duplication is applied to snapshots and clones, then storage capacity utilization is improved, but complexity of space management increases due to reference counting mechanisms
Solution Approach 1:
The patent introduces space adjustment counters as intermediary elements that mediate between the complex reference counting mechanisms and the space savings reporting function. These counters act as simplified interfaces that automatically track and adjust for the space consumed by metadata and reference structures, shielding users from the underlying complexity of reference counting while enabling accurate de-duplication-based space utilization reporting.
Data Source
AI summary
A technique efficiently determines accurate storage space savings reported to a host coupled to a reference-counted storage system that employs de-duplication and compression, wherein the storage space savings relate to snapshots and/or clones supported by the storage system. The snapshot/clone may be represented as an independent volume, and embodied as a respective read-only copy (snapshot) or read-write copy (clone) of a parent volume. Metadata is illustratively organized as one or more multi-level dense trees, wherein each level of each dense tree includes volume metadata entries for storing the metadata. The metadata is illustratively embodied as mappings from LBAs of a LUN to extent keys. Space adjustment counters, such as clone space adjustment (CSA) and diverged space adjustment (DSA) counters, may be employed when determining the storage space savings. The CSA counter is equal to the sum of mapped storage space across all levels of a dense tree. The DSA counter for the clone and for the snapshot equals the total mapped storage space in the level. The storage space savings may be determined by computing a value equal to the addition of the CSA counter to the total amount of data and metadata written to the LUN minus the DSA counters and, thereafter, dividing the value by the total amount of de-duplicated and compressed data for the LUN that is physically stored.