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Challenge 14: Storage Redundancy & Tiers

Estimated Time

20-30 min | Cost: Free | Domain: Azure Architecture & Services (35-40%)

Exam skills covered​

  • Describe storage tiers (hot, cool, cold, archive)
  • Describe redundancy options (LRS, ZRS, GRS, RA-GRS)

Overview​

Azure Storage keeps multiple copies of your data to protect against failures. The redundancy option you choose determines how many copies are made and where they're stored. Azure also offers access tiers that let you optimize costs based on how frequently data is accessed.

Explore​

Task 1: Understand redundancy options​

RedundancyCopiesScopeProtects against
LRS (Locally Redundant)3Single datacenterDisk/rack failure
ZRS (Zone Redundant)33 availability zonesDatacenter failure
GRS (Geo-Redundant)63 local + 3 in paired regionRegional failure
RA-GRS (Read-Access GRS)6Same as GRS + read from secondaryRegional failure + read availability
GZRS (Geo-Zone Redundant)63 zones + 3 in paired regionZone + regional failure
RA-GZRS6Same as GZRS + read from secondaryMaximum protection

Visual representation:

LRS:    [Copy1][Copy2][Copy3]  ← All in ONE datacenter

ZRS:    [Zone1]  [Zone2]  [Zone3]  ← Each in a DIFFERENT datacenter

GRS:    [Primary: 3 copies] ←→ [Secondary region: 3 copies]

RA-GRS: Same as GRS, but secondary is READABLE

Task 2: Choose redundancy for scenarios​

ScenarioRecommended redundancyWhy
Dev/test, non-critical dataLRSCheapest, single datacenter OK
Production web app dataZRSSurvives datacenter failure
Disaster recovery / complianceGRS or RA-GRSSurvives regional failure
Mission-critical dataRA-GZRSMaximum durability + read availability

Task 3: Understand access tiers​

TierAccess frequencyStorage costAccess costMin duration
HotFrequently accessedHigherLowerNone
CoolInfrequently (≥30 days)LowerHigher30 days
ColdRarely (≥90 days)Lower stillHigher still90 days
ArchiveAlmost never (≥180 days)LowestHighest + rehydration time180 days

Cost trade-off: Cheaper to store ↔ More expensive to access

Task 4: Access tier scenarios​

Data typeBest tierReasoning
Active website imagesHotAccessed constantly
Monthly reports (current quarter)CoolAccessed occasionally
Compliance data (yearly audit)ColdRarely accessed
7-year backup archivesArchiveAlmost never accessed

Archive tier details:

  • Data is stored offline
  • Rehydration can take hours (up to 15 hours for standard)
  • Priority rehydration available (under 1 hour, costs more)
  • Cannot read data directly — must rehydrate first

Task 5: Explore in the Portal​

  1. In Azure Portal, search for Storage accounts → + Create
  2. On the Basics tab, observe:
    • Redundancy dropdown: LRS, ZRS, GRS, RA-GRS, GZRS, RA-GZRS
  3. On the Advanced tab, observe:
    • Default access tier: Hot, Cool, or Cold
  4. Click Cancel
Azure CLI Alternative
# Check storage account redundancy (if one exists)
az storage account list --query "[].{Name:name, Redundancy:sku.name}" --output table

# Access tier is set per blob or per account default
# Example: change a blob tier (requires a storage account)
# az storage blob set-tier --account-name <name> --container-name <container> --name <blob> --tier Cool

Key Concepts​

ConceptDescription
LRS3 copies in one datacenter (cheapest, least durable)
ZRS3 copies across availability zones
GRS3 local + 3 in paired region (cross-region protection)
RA-GRSGRS + read access to secondary region
Hot tierOptimized for frequent access
Cool tierLower storage cost, higher access cost (30-day minimum)
Cold tierEven lower storage cost (90-day minimum)
Archive tierLowest storage cost, offline data (180-day minimum)

Knowledge Check​

1. A company needs to ensure their data survives a complete regional outage. Which minimum redundancy option should they choose?

2. Data that must be retained for 7 years for compliance but is almost never accessed should be stored in which tier?

3. What is a key limitation of the Archive access tier?

4. LRS stores how many copies of your data?

5. What is the difference between GRS and RA-GRS?

Learn More​