Snapshot Restore Workflow for Storage Containers
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Solution Overview
Problem
Existing storage systems face challenges in efficiently restoring snapshots of storage containers without disrupting hosts, as they often require removing or re-identifying logical units (LUNs), which can lead to outages or crashes.
Innovation Solution
A snapshot restore technique that creates a read-write clone of the snapshot, replaces the active volume with the clone, deletes the old active volume, and maps the LUN to the clone, using a distributed cluster database to update attributes and maintain host identity, performed in an atomic operation within the storage I/O stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing storage system removes or re-identifies LUNs to restore snapshots, then the snapshot restoration can be completed, but host outages or crashes occur
Solution Approach 1:
The system segments the snapshot restoration process into distinct operations: creating a clone volume from the snapshot, replacing the active volume with the clone, deleting the old active volume, and mapping the LUN to the clone. This segmentation allows the restoration to proceed without removing the LUN from the host, maintaining host continuity while achieving snapshot restoration.
Solution Approach 2:
The patent introduces a clone volume as an intermediary between the snapshot and the active volume. The clone serves as a mediator that allows the LUN to be restored to a previous state without directly modifying or removing the original LUN mapping, thus avoiding host outages while enabling snapshot restoration.
2Productivity
If the LUN identity is changed during snapshot restoration, then the restoration can be completed, but host disruption occurs
Solution Approach 1:
The system performs preliminary actions by creating the clone volume from the snapshot before replacing the active volume. This preliminary clone creation allows the restoration process to be prepared in advance, enabling quick replacement and LUN remapping without changing the LUN identity, thus achieving fast restoration without host disruption.
Solution Approach 2:
Instead of modifying the original LUN identity during restoration, the patent inverts the approach by creating a new clone volume that inherits the LUN mapping. The LUN is then remapped to the clone, preserving the original LUN identity while achieving restoration, thereby avoiding host disruption.
3Reliability
If complex operations are used to restore snapshots, then complete restoration is achieved, but system complexity increases
Solution Approach 1:
The patent merges multiple basic storage operations (snapshot creation, clone creation, volume replacement, volume deletion, and LUN remapping) into a coordinated snapshot restoration process. By combining these fundamental operations that the storage system already supports, the system achieves complete snapshot restoration without introducing complex specialized operations, thus maintaining system simplicity while ensuring restoration completeness.
Data Source
AI summary
A snap restore technique efficiently restores snapshots of storage containers served by a storage input/output (I/O) stack executing on one or more nodes of a cluster. A Small Computer Systems Interface administration layer interacts with a volume layer of the storage I/O stack to manage and implement a snap restore procedure to restore one or more snapshots of a storage container. The storage container may be a logical unit (LUN) embodied as parent volume (active volume) and the snapshot may be represented as an independent volume embodied as read-only copy of the active volume. The snap restore procedure may be configured to allow restoration to a single snapshot of a LUN or restoration of a plurality of LUNs organized as a consistency group from a group of snapshots. Restoration of the LUN from a snapshot involves (i) creation of another independent volume embodied as a read-write copy (clone) of the snapshot, (ii) replacement of the (old) active volume with the clone, (iii) deletion of the old active volume, and (iv) mapping of the LUN to the clone (i.e., a new active volume).