Interview prep · 🗄️ Backup & Storage Engineer
Backup & Storage Engineer interview questionsand answers (30, by level).
The questions Indian employers actually ask for this role — fresher, mid-level and senior — with model answers written by engineers who sit on the other side of the table. Use with the role path and the 30-day lab plan.
Fresher / L1
Fundamentals they test on day one
1What is the 3-2-1 backup rule?
Three copies, on two media types, one offsite (today: plus one offline/immutable copy — 3-2-1-1-0 with zero restore errors).
2RPO vs RTO?
RPO: how much data you can lose (time since last backup). RTO: how long to restore service. They drive backup frequency and DR design.
3Full, incremental, differential backups?
Full copies everything; incremental copies changes since last backup of any type; differential copies changes since last full. Trade-off between backup speed and restore complexity.
4RAID 1, 5, 6, 10 — differences?
RAID1 mirror; RAID5 single parity (one disk failure); RAID6 double parity; RAID10 mirrored stripes (fast rebuild, 50% capacity). Avoid RAID5 on large disks.
5What is a snapshot and is it a backup?
Point-in-time view at the storage layer; not a backup because it lives on the same storage — good for quick rollback, must be copied elsewhere.
6SAN vs NAS vs DAS?
SAN: block over FC/iSCSI; NAS: file over NFS/SMB; DAS: disks attached directly. Choose by access pattern and sharing needs.
7What is deduplication and compression?
Dedup stores identical blocks once (big wins for VM backups); compression shrinks data; both reduce storage cost at some CPU expense.
8What is LUN masking and zoning?
Zoning (FC switch) controls which WWNs can see each other; masking (array) controls which hosts see which LUNs.
9How do you verify a backup actually works?
Scheduled restore tests, verification jobs (checksums), restore a VM to an isolated network, document results.
10IOPS, throughput, latency — define.
IOPS: operations per second (random workloads); throughput: MB/s (sequential); latency: time per operation (what users feel).
2–5 years / L2
What a working engineer must know
1Design backups for 50 VMs on Proxmox with offsite copy.
PBS with daily incremental-forever, dedup, verify jobs, prune (7 daily/4 weekly/6 monthly), sync to a remote PBS over WAN, encryption at rest, restore tests monthly.
2How does Veeam application-aware processing work?
Uses VSS inside Windows guests to quiesce apps (SQL, Exchange, AD) for consistent backups and log truncation.
3Immutable backups — how do you achieve them?
Object lock (S3/MinIO), Linux hardened repository, PBS with restricted users, tape/air-gap; ensures ransomware cannot delete backups.
4Ceph: pools, PGs, replication vs erasure coding?
Pools hold objects; PGs distribute them across OSDs; replication (3×) is simpler and faster; EC saves space with more CPU/latency — for cold data.
5ZFS features that matter in production?
Checksums with self-healing, snapshots/clones, send/receive replication, ARC/L2ARC caching, compression; ensure ECC RAM and avoid >80% full pools.
6Explain multipathing.
Multiple paths from host to SAN LUN (two HBAs, two fabrics); MPIO/multipathd provides failover and load balancing; verify path counts after changes.
7How do you size storage for a new VM cluster?
Current used + growth (3 yr), snapshot/backup overhead, RAID/replication factor, performance (IOPS per VM), tiering; our Proxmox sizer does this.
8Backup window keeps overrunning — options?
Incremental-forever/CBT, more concurrency/proxies, faster target (NVMe/dedup appliance), stagger jobs, exclude swap/temp, network upgrade, synthetic fulls.
9NFS vs iSCSI for VM storage?
NFS: simpler, file-level, easy snapshots; iSCSI: block, often faster for databases, needs LVM/clustered FS on shared LUNs. Both fine at 10/25 GbE.
10How do you migrate data between two SANs with minimal downtime?
Host-based mirroring (LVM/ZFS), storage vMotion/Proxmox move-disk live, array replication then cutover, or rsync for file shares with final delta sync.
Senior / L3
Design, judgement and leadership
1Design a DR strategy for RPO 15 min / RTO 2 h across two Indian cities.
Async storage/VM replication (ZFS send, Ceph RBD mirror, Veeam CDP), DNS/BGP failover plan, runbooks, quarterly DR drills, capacity at DR for critical tier, data consistency for databases (log shipping).
2Ransomware recovery plan — what do you need in place beforehand?
Immutable/offline copies, clean-room restore network, known-good images, credential isolation for backup system, tested restore order (AD first), communication plan.
3Tape in 2026 — still relevant?
Yes for air-gap and cheap long-term retention (LTO-9/10, ~18–36 TB native); use for monthly/yearly copies and compliance.
4How do you set retention policy for a regulated company?
Map to legal requirements (tax 8 yrs, SEBI/RBI rules), business needs, cost; GFS scheme; document and automate deletion; legal hold capability.
5Storage performance issue: how do you find the bottleneck?
Latency per layer (guest, hypervisor, network/FC, array), queue depths, IOPS vs limits, noisy neighbour, cache hit ratio, path imbalance, firmware; iostat/esxtop/Prometheus.
6Compare Ceph vs enterprise SAN for a 300-VM private cloud.
Ceph: scale-out, no vendor lock-in, needs skills and 25 GbE; SAN: predictable latency, support contracts, higher cost per TB, FC skills. Hybrid common.
7How do you test backups at scale without manual effort?
Automated restore verification (SureBackup-style, PBS verify + scripted VM boot tests), checksum audits, reporting dashboards, alerts on missed jobs.
8Object storage (S3/MinIO) use cases on-prem?
Backup targets with object lock, archives, application assets, log retention; cheaper per TB, 11-nines durability design with erasure coding.
9Capacity planning and procurement cycle?
Trend p95 growth, thresholds (70/80/90%), lead times (8–16 weeks in India), TCO over 5 years, support renewals, compatibility matrices.
10A restore failed during a real incident — what do you do and change?
Escalate alternate copies, partial restores, vendor support; afterwards: root cause (verification gap, media), add verify jobs, change RPO/retention, update runbook.
How to answer
Four habits that pass interviews
- Say the structure first“I’d check three things: …” — interviewers reward a method more than a lucky answer.
- Numbers and namesMention real tools, versions and figures from your lab; vague answers lose.
- Admit gaps cleanly“I haven’t run X in production; here is how I’d approach it” beats bluffing.
- Ask about the environmentScale, on-call, tooling — it shows you think like an operator.
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