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Difficulty: MediumData Redundancy and High Availability

A company is migrating a legacy stateful application to Azure. The application runs on a single Azure Virtual Machine (VM) and requires high-performance block storage for its database. The database does not support application-level replication. The storage solution must meet the following requirements:
- Maintain read and write availability if a single Azure datacenter or availability zone fails.
- Experience zero data loss (RPO = 0) in the event of a zone outage.
- Provide high-performance storage suitable for database transaction logs.

Which disk configuration should you recommend?

  1. A
    Premium SSD Managed Disks configured with Locally Redundant Storage (LRS)
  2. B
    Standard HDD Managed Disks configured with Zone-Redundant Storage (ZRS)
  3. Premium SSD Managed Disks configured with Zone-Redundant Storage (ZRS)Answer
  4. D
    Premium SSD Managed Disks configured with Geo-Redundant Storage (GRS)

Answer

Premium SSD Managed Disks configured with Zone-Redundant Storage (ZRS)
Premium SSD Managed Disks configured with Zone-Redundant Storage (ZRS) provide the necessary high performance for database transaction logs while replicating data synchronously across three availability zones in the primary region. This ensures that the storage remains accessible and suffers zero data loss if a single availability zone goes offline.

Step-by-Step Solution

1
Analyze performance requirements.
Database transaction logs require high-performance block storage, ruling out Standard HDD storage due to performance limitations.
Databases need high IOPS and throughput to prevent performance bottlenecks.
2
Evaluate availability and data loss constraints.
The storage must survive a single availability zone failure with zero data loss (RPO = 0). This eliminates Locally Redundant Storage (LRS) since it is confined to a single datacenter.
LRS does not replicate data across availability zones.
3
Check capability support for Azure Managed Disks.
Azure Managed Disks only support LRS and ZRS natively. Geo-Redundant Storage (GRS) is not supported for managed disks, eliminating GRS.
Azure Managed Disks do not have native geo-replication options at the disk configuration tier.

Key Concept

Selecting the appropriate storage redundancy tier for Azure Managed Disks based on performance, availability, and capability support constraints.
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Topics

Data Redundancy and High Availability

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