Snapshot Object Durability via Delayed Deletion and Recovery
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Solution Overview
Problem
Cloud-based snapshot storage systems face issues with erroneous deletion of snapshot objects, leading to irretrievable loss of data due to software bugs or hardware issues, as they incorrectly determine that objects are not referenced by active snapshots, resulting in premature physical deletion.
Innovation Solution
Implementing a snapshot durability system that delays physical deletion of snapshot objects, periodically analyzes stored and active snapshot objects, and recovers missing objects before they are permanently deleted, using a 'soft delete' mechanism and maintaining metadata to track objects' availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If snapshot objects are deleted immediately when not referenced by active snapshots, then storage space is freed quickly, but data loss occurs due to erroneous deletion
Solution Approach 1:
The system performs preliminary actions by marking snapshot objects for deletion rather than immediately deleting them. A soft-delete mechanism is implemented where objects are flagged and scheduled for deletion after a delay period, allowing recovery opportunities before permanent removal. This preliminary marking action prevents erroneous deletions while maintaining storage efficiency.
Solution Approach 2:
The system implements beforehand cushioning by introducing a recovery window between the deletion decision and actual deletion execution. During this window, the system periodically checks whether deleted objects should be recovered based on their reference status. This cushioning period protects against data loss from erroneous deletion decisions while still enabling eventual cleanup.
2Reliability
If a recovery mechanism is implemented for deleted snapshot objects, then data durability is improved, but system complexity increases
Solution Approach 1:
The recovery mechanism leverages existing universal components of the snapshot management system. The same reference tracking infrastructure used for normal snapshot operations is also employed to identify recoverable objects. The periodic analysis function serves dual purposes: monitoring active snapshots and identifying objects needing recovery, avoiding the need for separate complex recovery systems.
Solution Approach 2:
The system implements self-service by automatically detecting and recovering erroneous deletions without external intervention. The periodic analysis process autonomously identifies snapshot objects that should be recovered based on their reference status and restores them automatically. This self-service approach improves data durability while minimizing operational complexity through automation.
3Reliability
If snapshot objects are retained longer before deletion, then recovery opportunities increase, but storage space remains occupied longer
Solution Approach 1:
The system employs periodic action by conducting regular analysis cycles to review the status of marked-for-deletion objects. Instead of continuous monitoring, the system performs analysis at scheduled intervals during the retention period. This periodic approach balances recovery opportunities with storage optimization, allowing objects to be retained long enough for recovery if needed while eventually freeing space through systematic cleanup.
Data Source
AI summary
Systems and methods for durable storage of storage volume “snapshots” are provided. Snapshots are stored as collections of snapshot data objects. To improve the durability of snapshot storage, physical deletion of snapshot data objects may be delayed for a period of time after the snapshot data objects are marked for deletion. Lists of the stored snapshot data objects and the snapshot data objects that make up active snapshots may be periodically analyzed. If there are any snapshot data objects that are part of active snapshots and are not present in the list of stored snapshot data objects, the snapshot data objects may be recovered before they are physically deleted.