AZ-305 Design infrastructure solutions Practice Question
An organization is designing a storage solution for Azure VMs running a database that requires low latency and high IOPS. The data is critical and must be durable with automatic replication across multiple datacenters in the same region. Which Azure managed disk type and redundancy option should they choose?
⚠ Common exam trap
A common mix-up: candidates confuse ZRS with GRS, assuming that 'redundancy across multiple datacenters' requires geo-replication, but ZRS provides intra-region zone redundancy without the latency penalty of asynchronous geo-replication.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Premium SSD with ZRS
Premium SSD with ZRS is correct because the database requires low latency and high IOPS, which Premium SSD provides, and ZRS (Zone-Redundant Storage) automatically replicates data synchronously across three Azure availability zones within the same region, ensuring durability and high availability without the cross-region latency of GRS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Standard SSD with GRS
Why it's wrong here
Standard SSDs deliver lower and more variable IOPS/latency than Premium SSDs, making them a poor fit for a production VM with consistent performance requirements. More fundamentally, GRS (geo-redundant storage) is not a supported redundancy option for Azure managed disks—it applies only to blob, file, queue, and table storage in general-purpose storage accounts, not to disk blobs behind a VM. Since the question demands both high performance and multi-datacenter resilience, this combination fails on both axes.
- ✓
Premium SSD with ZRS
Why this is correct
Premium SSDs provide high IOPS (up to 20,000 per disk, depending on size) and low single-digit millisecond latencies, ideal for I/O-intensive workloads. With ZRS, the disk synchronously writes three replicas across three Azure availability zones within the same region, so the VM can survive an entire datacenter or zone failure while retaining the performance characteristics needed. This combination is directly supported for managed disks and precisely satisfies the stated requirement for high performance and replication across multiple datacenters.
- ✗
Ultra Disk with LRS
Why it's wrong here
Ultra Disks offer the highest IOPS and latency performance of any Azure managed disk (up to 160,000 IOPS per disk), but they support only locally redundant storage (LRS), meaning the data is triple-written to a single datacenter within a region. LRS does not protect against a datacenter-wide outage, so despite its outstanding performance, it fails the multi-datacenter resilience requirement. Furthermore, Ultra Disks are not supported with ZRS or any geo-replication option, making them unsuitable for this design.
- ✗
Premium SSD v2 with LRS
Why it's wrong here
Premium SSD v2 is a newer disk offering that provides higher IOPS/throughput per cost than standard Premium SSD, with per-disk provisioning of performance, but currently only supports LRS. LRS replicates data three times within a single datacenter, so a fire, flood, or other datacenter-level failure would interrupt availability and potentially cause data loss. Since the intended design requires multi-datacenter redundancy, Premium SSD v2's lack of ZRS support eliminates it even though its performance could otherwise suffice.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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