What is used by Dell Avamar to provide system-wide fault tolerance?

Dell Avamar ensures high availability and data integrity through multiple layers of fault tolerance. RAID (Redundant Array of Independent Disks) protects against individual disk failures within a node. RAIN (Redundant Array of Independent Nodes) protects against the failure of an entire storage node by distributing data and parity across the grid. Checkpoints are validated point-in-time snapshots of the server's metadata, enabling rollback capabilities. Replication provides disaster recovery by copying backup data to a secondary Avamar system.

B. HFS check: HFS check (hfscheck) is a maintenance utility for checking file system integrity, not a built-in, continuous fault tolerance mechanism.
C. Asynchronous crunching: This is not a recognized Avamar fault tolerance term. Parity is a component of RAID and RAIN, not a separate mechanism.
D. HFS check: As stated previously, HFS check is a reactive maintenance tool, not a primary, proactive fault tolerance feature like the others listed.

- Dell Avamar 19.4 Administration Guide, Page 416, "Data protection". This section details the roles of Checkpoints, RAIN, and Replication in protecting the Avamar server.

- Dell EMC Avamar Data Store Gen4S Hardware Information Guide. This document describes the physical node architecture, which includes RAID-protected disks as a fundamental component.

- Dell Technologies White Paper: "Dell EMC Avamar—Data Protection and Recovery". This paper provides a detailed overview of Avamar's reliability features, including RAIN for node-level protection and replication for disaster recovery.