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📘Microsoft Certified: Azure Administrator Associate (AZ-104)
Managing Virtual Machine (VM) sizes and disks is a key skill for an Azure Administrator. In this part of the exam, you must understand how VM sizes work, how to resize VMs, disk types, disk performance, and how to manage and optimize Azure disks.
This section ensures you can select the right VM size for performance, scale your VM when workload changes, and configure storage that meets requirements for capacity, speed, backup, and security.
1. Understanding VM Sizes in Azure
Azure VMs come in predefined sizes, and each size determines:
- Number of vCPUs
- Amount of RAM
- Storage throughput limits
- Network performance
- Supported features (e.g., premium SSD support, GPU support)
Different business applications require different VM capabilities, so choosing the right VM size is important.
1.1 VM Size Categories
Azure groups VM sizes into families, each designed for a specific workload.
A. General Purpose
- Balanced CPU, RAM, and storage.
- Best for:
- Web servers
- Small databases
- Application servers
Examples: B-series, Dsv5, Dv5
B. Compute Optimized
- High CPU-to-memory ratio.
- Best for:
- Batch processing
- Medium traffic web servers
- Development and testing
Example: Fsv2-series
C. Memory Optimized
- More RAM per CPU.
- Best for:
- Large databases
- In-memory caching
- Big data applications
Example: Esv5-series
D. Storage Optimized
- High disk throughput and IOPS.
- Best for:
- Big data analytics
- SQL/NoSQL databases
- Log processing
Example: Lsv3-series
E. GPU VMs
- Designed for graphics-heavy or AI workloads.
- Best for:
- Machine learning
- 3D rendering
- Video processing
Example: NC, ND, NV
F. High Performance Computing (HPC)
- Very fast CPU performance, low latency.
- Used for:
- Scientific simulations
- Engineering workloads
Example: H-series
1.2 How to Check Available VM Sizes
You can check which VM sizes are available in a region or on a specific host:
Azure Portal
- Go to VM → Size
- The portal displays only available options in your region.
Azure CLI
az vm list-sizes --location eastus
Important Exam Tip
Some VM sizes support only Premium SSDs, Ephemeral OS disks, Accelerated Networking, or Generation 2 VMs.
1.3 Resizing a VM
A VM can be resized if:
- The new size is available in that region
- The current hardware cluster supports the new size
Resizing may require a reboot
- Same hardware cluster → no downtime
- New cluster required → VM must stop and deallocate
Steps to Resize (Portal)
- Go to VM → Size
- Select a new size
- Click Resize
Azure CLI
az vm resize \
--resource-group MyRG \
--name MyVM \
--size Standard_D4s_v5
Exam Tip
- If resizing fails, you must stop (deallocate) the VM first.
- Deallocation releases the host, allowing Azure to move the VM to another cluster with your desired size.
2. Understanding Azure VM Disks
Azure VMs use different types of managed disks to store OS, data, and temporary files.
2.1 Types of Disks
A. OS Disk
- Contains the operating system (Windows or Linux)
- Supports encryption, snapshots, backups
- Typically 64 GB – 127 GB, but can be larger
B. Data Disks
- Additional disks for storing applications, databases, logs, etc.
- Can attach multiple data disks depending on the VM size
C. Temporary Disk
- Local disk on the host machine
- Used for pagefile, swap, and temporary data
- Data is lost if the VM moves to a new host
- Not backed up
3. Azure Managed Disk Types
Azure offers several disk types optimized for capacity, performance, and cost.
Understanding these is crucial for the exam.
3.1 Standard HDD
- Lowest cost
- Lowest performance
- Suitable for:
- Light workloads
- Test environments
3.2 Standard SSD
- Better performance than HDD
- Cost-effective
- Ideal for:
- Web servers
- Low-traffic applications
3.3 Premium SSD
- High performance, low latency
- Required for many production workloads
- Good for:
- SQL database
- High IOPS applications
- Enterprise workloads
Premium SSD v2 (Latest generation)
- Even higher throughput and IOPS
- Configurable performance levels
3.4 Ultra Disk
- Highest performance disk type
- Extremely high IOPS and throughput
- Best for:
- High-performance databases
- Massive data writes
- Transaction-heavy workloads
4. Disk Performance Concepts
Disk performance is measured by:
IOPS (Input/Output Operations Per Second)
- Number of read/write operations per second
Throughput
- Amount of data transferred per second (MB/s)
Latency
- Time taken to complete a storage request
Azure limits disk performance based on:
- Disk type
- Disk size
- VM size (VM also has IOPS caps)
5. Attaching and Detaching Data Disks
Attach a disk in the Portal
- Go to VM → Disks
- Click Add data disk
- Choose Create new or Attach existing
- Save
CLI
az vm disk attach \
--vm-name MyVM \
--resource-group MyRG \
--name MyDataDisk
Detach a disk
- Must unmount in OS first (Linux/Windows)
- Then remove via portal or CLI
6. Disk Encryption in VM Management
Azure supports:
Azure Disk Encryption (ADE) (OS-level)
- Uses BitLocker (Windows) or DM-Crypt (Linux)
Server-Side Encryption (SSE)
- Default
- Encrypts disk automatically
Customer-Managed Keys (CMK) support
- Encrypt disks with your own keys from Azure Key Vault
7. Resizing (“Upscaling”) Disks
Disks can be increased in size but cannot be reduced.
To resize:
- Stop VM (sometimes required)
- Go to Managed Disk → Size + performance
- Select new size
Use Case in IT
- A database grows and requires additional storage space
- Log files exceed capacity on a data disk
8. Disk Snapshots and Backups
Snapshots
- Point-in-time copy of a disk
- Useful before upgrading applications or performing changes
Azure Backup
- Full VM backup
- Recommended for production workloads
9. Ephemeral OS Disks
An Ephemeral OS disk is stored locally on the VM host instead of Azure Storage.
Features
- Very fast
- Best for stateless workloads
- Data lost if VM moves hosts
- Not supported for all sizes
Exam Tip: Use ephemeral OS disks only when the application can tolerate OS rebuilds.
10. Common IT Use Cases (Safe for Exam)
- Scaling VM size when a line-of-business application requires more CPU or RAM
- Using premium SSD for a production database server to ensure fast response times
- Using Standard SSD for a development VM because it needs better performance than HDD but at low cost
- Using temporary disk for OS paging to improve performance
- Creating snapshots before applying major software updates to avoid downtime if something breaks
11. Key AZ-104 Exam Tips
- Understand each disk type and its purpose
- Know how to resize VMs and what causes downtime
- Temporary disk is not persistent
- Ultra Disk requires explicit enabling and only certain VM sizes support it
- Disk resizing can only go up, never down
- VM performance depends on both disk type and VM size IOPS limit
- Premium SSDs require Premium Storage-supported VM sizes
Final Summary
To manage VM sizes and disks effectively in Azure:
- Select the correct VM size for your workload
- Understand the limits and capabilities of each size family
- Attach, detach, resize, and encrypt disks properly
- Know the characteristics and performance levels of HDD, SSD, Premium SSD, and Ultra disks
- Use snapshots and backups for disk protection
- Avoid storing important data on temporary disks
These skills are essential for real IT operations and are heavily tested on the AZ-104 exam.
