Storage Redundancy Checks

Overview

Storage accounts underpin Azure Functions, Container Apps (for host storage), and App Service. If compute is zone-redundant but storage is not, a zone failure can still cause downtime.

Replication Types

Type	Zone Redundancy	Region Redundancy	Description
LRS	❌ None	❌ None	3 copies in one datacenter. No zone or region protection.
ZRS	✅ Zone-redundant	❌ None	3 copies across 3 availability zones in one region.
GRS	❌ None (LRS per region)	✅ Region-redundant	LRS in primary + LRS in secondary region. Zone failure in primary = risk.
GZRS	✅ Zone-redundant	✅ Region-redundant	ZRS in primary region + LRS in secondary region. Best protection.
RA-GRS	❌ None (LRS per region)	✅ Region + read	Like GRS but secondary is readable. Still LRS within each region.
RA-GZRS	✅ Zone-redundant	✅ Region + read	GZRS + read access to secondary. Maximum redundancy.

Minimum Requirement

If compute is zone-redundant → storage MUST be at least ZRS (not GRS — GRS uses LRS in each region and is NOT zone-redundant)
For multi-region failover → storage should be GZRS (zone + region) or GRS (region only, accepts zone risk)

Resource Graph Queries

⚠️ Output format: Use --query "data[]" -o json (not -o table). az graph query -o table only renders summary columns and does not show projected fields.

Find All Storage Accounts and Their Replication

az graph query -q "
Resources
| where type =~ 'microsoft.storage/storageaccounts'
| extend replication = tostring(sku.name)
| extend tier = tostring(sku.tier)
| project name, resourceGroup, location, replication, tier, kind
| order by replication asc
" --query "data[]" -o json

💡 No SKU specified? If a storage account was deployed without an explicit sku.name (raw ARM/Bicep) or skuName (AVM module), Azure defaults to Standard_GRS. Treat any storage account showing Standard_GRS as potentially "defaulted" rather than intentionally chosen — check the IaC source to confirm and recommend setting it explicitly to Standard_ZRS or Standard_GZRS.

Find Storage Accounts Using LRS (Not Zone Redundant)

az graph query -q "
Resources
| where type =~ 'microsoft.storage/storageaccounts'
| where sku.name =~ 'Standard_LRS' or sku.name =~ 'Premium_LRS'
| project name, resourceGroup, location, replication=sku.name
" --query "data[]" -o json

Find Function App Host Storage Accounts

# List function apps and their storage connections
az graph query -q "
Resources
| where type =~ 'microsoft.web/sites'
| where kind contains 'functionapp'
| project name, resourceGroup, location
" --query "data[]" -o json

# Then for each function app, check its storage:
az functionapp config appsettings list \
  --name <app-name> \
  --resource-group <rg> \
  --query "[?name=='AzureWebJobsStorage'].value" -o tsv

Cross-Reference: Zone-Redundant Compute with Non-ZRS Storage

This is a critical gap detection query — zone-redundant compute paired with LRS storage:

# Step 1: Find zone-redundant plans
az graph query -q "
Resources
| where type =~ 'microsoft.web/serverfarms'
| where tobool(properties.zoneRedundant) == true
| project planName=name, resourceGroup, location
" --query "data[]" -o json

# Step 2: Check if associated storage accounts are ZRS
# (Requires app-level inspection of AzureWebJobsStorage setting)

Remediation

Upgrade Storage from LRS to ZRS

# Check if live migration is available (not all regions/account types support it)
az storage account show \
  --name <account-name> \
  --resource-group <rg> \
  --query "{name:name, sku:sku.name, kind:kind, location:location}"

# Request live migration (Standard_LRS → Standard_ZRS)
az storage account update \
  --name <account-name> \
  --resource-group <rg> \
  --sku Standard_ZRS

⚠️ Limitations:

Live migration from LRS to ZRS is only supported for Standard general-purpose v2 accounts
Premium accounts and legacy account types require manual migration (create new ZRS account + copy data)
Migration can take hours to days depending on data volume

Upgrade Storage from LRS to GRS/GZRS

# Upgrade to GRS
az storage account update \
  --name <account-name> \
  --resource-group <rg> \
  --sku Standard_GRS

# Upgrade to GZRS (zone + region redundant)
az storage account update \
  --name <account-name> \
  --resource-group <rg> \
  --sku Standard_GZRS

Reporting

For the reliability checklist, mark the ZRS Storage column per storage account:

✅ — SKU is Standard_ZRS or Standard_GZRS
❌ (LRS) — Standard_LRS (no zone redundancy)
❌ (GRS) — Standard_GRS or Standard_RAGRS (region-redundant but uses LRS in each region; still a zone-failure risk). Also flag this when no SKU is set in IaC at all — ARM/AVM defaults to Standard_GRS.

⚠️ Key distinction: GRS provides region redundancy but uses LRS in each region. If compute is zone-redundant but storage is GRS (not ZRS/GZRS), a zone failure can still impact storage availability.

/azure-reliability

referencesstorage-redundancy-checks.md