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Dell DCA-ISM study materials
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Dell DCA-ISM: Business Continuity: Backup, Replication, and Disaster Recovery

Dell DCA-ISM · Work through your exam, one topic at a time.

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Business Continuity: Backup, Replication, and Disaster Recovery

Business continuity questions are scenario-driven: you are given an outage, a change rate and a link, then asked which technology satisfies the RPO and RTO.

Definitions and technology boundaries

  • RPO is the tolerable data loss measured in time; RTO is the tolerable downtime. Both are business decisions that select the technology, not the reverse.
  • Backup is an independent point-in-time copy on separate media for restore. A snapshot is a pointer-based state on the same array and is not a backup. A replica is a live, continuously updated copy. Archive is long-term retention for compliance, not recovery.

Backup mechanics

  • Full plus incremental (changed since the last backup of any kind) or differential (changed since the last full); synthetic fulls build a new full from existing data; forever incremental avoids repeated fulls; GFS retention keeps daily, weekly and monthly points.
  • Deduplication is typically variable-length block, inline or post-process. PowerProtect DD with DD Boost shifts part of the dedupe work to the backup host; retention lock prevents expiry or deletion; PowerProtect Data Manager and NetWorker orchestrate policy.
  • The 3-2-1 rule: three copies, two different media, one offsite or offline. An air-gapped Cyber Recovery vault with anomaly detection is the ransomware-resistant version.

Replication

  • Synchronous replication acknowledges the host only after both arrays commit: RPO of zero, but latency-bound, so distance is limited to roughly single-digit milliseconds round trip.
  • Asynchronous replication acknowledges locally and ships changed data in cycles: RPO is approximately the cycle time plus in-flight data.
  • SRDF provides sync, async and Metro active-active stretch variants; RecoverPoint provides continuous data protection with a journal for any-point-in-time recovery and cross-site replication; VPLEX provides stretched access across sites.

Worked example

A source changes 60 GB per hour and the inter-site link is 1 Gb/s. 60 GB/h equals 480 Gb/h, or about 133 Mb/s, roughly 13% of the link. Asynchronous replication on a 15-minute cycle meets a one-hour RPO with headroom for a three-times burst. Synchronous replication over the same 40 ms round-trip link would add about 40 ms to every host write and break the application's latency budget.

Traps that cost marks

  • Claiming RPO of zero for asynchronous replication.
  • Presenting snapshots as backups; they fail with the source array.
  • Forgetting failback and untested runbooks, which destroy real RTO performance.