AZ-305 Design data storage solutions Practice Question
A company runs a SQL Server database on an Azure virtual machine. They need to increase the storage capacity and improve I/O performance for their transaction log. The current data disk is a standard HDD. They want to achieve higher IOPS and throughput without increasing the size of the VM (the VM size supports up to 8 data disks). The database workload is write-intensive on the transaction log. Which configuration should they implement?
⚠ Common exam trap
A common mix-up: candidates think striping (Option A) or mirroring (Option C) with premium disks is needed for performance, but for a single transaction log file, a single premium SSD is sufficient and simpler, while mirroring adds unnecessary write overhead and striping with HDDs still yields poor IOPS.
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
✓
Replace the standard HDD disk with a premium SSD disk for the log drive
Replacing the standard HDD with a premium SSD directly addresses the need for higher IOPS and throughput for a write-intensive transaction log. Premium SSDs provide consistent low-latency performance and significantly higher IOPS/throughput compared to standard HDDs, without requiring a VM size change. Since the VM supports up to 8 data disks, a single premium SSD can meet the performance requirements more effectively than adding more HDDs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add additional standard HDD disks and configure a storage pool with simple (striping) layout
Why it's wrong here
Adding more Standard HDDs and combining them into a Storage Space with a simple (striping) layout does not materially improve transactional log performance. Azure Standard HDDs are capped at roughly 500 IOPS per disk and have high rotational latency; striping only distributes I/O across disks and cannot reduce the per-write latency that a serial, write-ahead log requires. In fact, the Storage Spaces software layer adds CPU and I/O overhead, and a simple (no parity) layout provides no fault tolerance if a disk fails. This approach remains far below the low-latency, high-IOPS characteristics needed for a write-intensive log drive.
- ✓
Replace the standard HDD disk with a premium SSD disk for the log drive
Why this is correct
Replacing the Standard HDD with a Premium SSD for the log drive directly addresses the bottleneck because SQL Server transaction log writes are serial and must be durable before a transaction is acknowledged; even modest write latency directly lengthens commit times. Azure Premium SSDs deliver per-disk IOPS and throughput up to an order of magnitude higher than Standard HDDs, with consistent single-digit-millisecond latencies (and sub-millisecond with burst). This change also guarantees predictable performance levels via the Azure disk SLA, allowing the log I/O path to keep pace with checkpoint and commit activity without introducing any additional software layers. It is the most appropriate, focused action for a write-intensive log workload on an Azure VM.
- ✗
Add a premium SSD disk and configure a storage space with mirroring for the log drive
Why it's wrong here
Adding a premium SSD disk improves IOPS and throughput, but configuring Storage Spaces with mirroring on the same VM introduces software-based write overhead, which negates the latency benefit for a write-intensive transaction log. This option is tempting because mirroring provides redundancy, and in a scenario prioritising fault tolerance over raw I/O performance, it would be correct.
- ✗
Use Azure Disk Encryption to improve performance
Why it's wrong here
Azure Disk Encryption (ADE) uses BitLocker on Windows (or DM-Crypt on Linux) to encrypt the OS and data disks at rest; it performs encryption/decryption in the VM's CPU or via the VM's virtualization stack, which adds computational overhead and can slightly reduce I/O throughput, especially for small random writes. It does nothing to increase disk IOPS, lower access latency, or enlarge the I/O queue depth, so it cannot improve performance. Azure already provides encryption at rest by default with Storage Service Encryption (SSE) for managed disks, so ADE is purely an additional security/control measure, not a performance tuning option.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-305 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-305 exam.