VMware Disk Provisioning Types: Complete Comparison Guide#

How It Works#

• Allocates storage space on-demand as the guest OS writes data
• Initially creates a small VMDK file that grows as needed
• Returns unused space to the datastore when files are deleted (with proper tools)

Advantages#

• Maximum storage efficiency - only uses space actually needed
• Fast VM deployment - minimal initial storage allocation
• Storage overcommitment - provision more VMs than physical storage
• Automatic space reclamation - can return unused space

Disadvantages#

• Performance degradation - slower performance as disk fills up
• Storage monitoring required - risk of running out of space
• Fragmentation - may lead to disk fragmentation over time
• No data security - previous data may still exist on storage blocks

Best Use Cases#

1
✅ Development and testing environments
2
✅ VDI deployments with many similar desktops
3
✅ Environments with limited storage
4
✅ Non-critical workloads
5
✅ Template VMs and rapid deployment scenarios

How It Works#

• Pre-allocates all storage space at VM creation time
• Does not zero out the allocated blocks initially
• Zeros blocks on first write by the guest OS

Advantages#

• Predictable storage usage - known disk space consumption
• Better performance than thin - no need for space allocation during writes
• Good for capacity planning - clear storage requirements
• Faster than eagerly zeroed - quicker VM creation

Disadvantages#

• Storage inefficiency - allocates full disk space even if unused
• First write penalty - slower performance on initial writes
• No space reclamation - cannot return unused space
• Security concerns - old data remains until overwritten

Best Use Cases#

1
✅ Production environments with predictable storage needs
2
✅ Applications requiring consistent performance
3
✅ Environments where storage planning is critical
4
✅ Medium-performance database workloads
5
✅ Backup and archival systems

How It Works#

• Pre-allocates all storage space at VM creation time
• Immediately zeros out all allocated blocks
• Provides the highest level of security and performance

Advantages#

• Best performance - no allocation or zeroing overhead during runtime
• Maximum security - all blocks are zeroed, eliminating data remnants
• Predictable behavior - consistent performance characteristics
• Compliance friendly - meets strict security requirements
• Optimal for clustering - best choice for clustered environments

Disadvantages#

• Longest creation time - significant time to zero all blocks
• Storage inefficiency - uses full allocated space immediately
• No flexibility - cannot overcommit storage
• Resource intensive - high I/O during creation process

Best Use Cases#

1
✅ High-performance databases (Oracle, SQL Server, MySQL)
2
✅ Security-sensitive environments
3
✅ Mission-critical applications
4
✅ High-IOPS workloads
5
✅ VMware vSphere clusters (vMotion, HA)
6
✅ Environments requiring data compliance (HIPAA, PCI-DSS)
7
✅ Production email servers
8
✅ ERP systems

Choose Thin Provisioned when:#

• Storage efficiency is the primary concern
• Working with development/test environments
• Need to maximize VM density
• Storage budget is constrained
• Performance requirements are flexible

Choose Thick Provisioned (Lazily Zeroed) when:#

• Need predictable storage usage
• Performance is important but not critical
• Want faster VM creation than eagerly zeroed
• Don’t need the highest security level
• Working with standard production workloads

Choose Thick Provisioned (Eagerly Zeroed) when:#

• Performance is the top priority
• Security requirements are strict
• Working with mission-critical applications
• Need compliance with data security standards
• Budget allows for premium storage usage
• Using VMware clustering features extensively

I/O Patterns Comparison#

1
graph LR
2
    A[Write Request] --> B{Provisioning Type}
3
    B -->|Thin| C[Check Space Available]
4
    B -->|Lazy Zero| D[Zero Block on First Write]
5
    B -->|Eager Zero| E[Direct Write]
6

7
    C --> F[Allocate New Block]
8
    F --> G[Zero Block]
9
    G --> H[Write Data]
10

11
    D --> I[Write Data]
12
    E --> J[Write Data - Fastest]
13

14
    H --> K[Complete - Slowest]
15
    I --> L[Complete - Medium]
16
    J --> M[Complete - Fastest]

Performance Benchmarks (Typical Results)#

Data Remnant Analysis#

Security Best Practices#

1. For Sensitive Data: Always use Thick Provisioned, Eagerly Zeroed
2. Multi-tenant Environments: Avoid thin provisioning for security isolation
3. Decommissioning: Proper disk wiping procedures regardless of provisioning type
4. Encryption: Consider vSAN encryption or VM-level encryption for additional security

Monitoring and Alerts#

1
# PowerCLI script to monitor thin provisioned disks
2
Get-VM | Get-HardDisk | Where-Object {$_.StorageFormat -eq "Thin"} |
3
Select-Object Parent, Name, CapacityGB, @{N="UsedSpaceGB";E={[math]::Round($_.ExtensionData.Summary.Committed/1GB,2)}}

Capacity Planning#

1. Thin Provisioning: Monitor at 70% utilization, plan for 2-3x overcommit ratio
2. Thick Provisioning: Standard 1:1 ratio, plan for growth
3. Mixed Environments: Separate storage tiers for different provisioning types

Migration Strategies#

1
# Convert thin to thick eager using PowerCLI
2
Get-VM "VMName" | Get-HardDisk | Set-HardDisk -StorageFormat EagerZeroedThick -Confirm:$false

Total Cost of Ownership Factors#

Best Overall Recommendation:#

• If you need maximum performance and have adequate storage → Thick Provisioned (Eagerly Zeroed)
• If you want a balance of performance and space efficiency → Thick Provisioned (Lazily Zeroed)
• If storage efficiency is critical and performance is flexible → Thin Provisioned

Enterprise Environment Strategy:#

1. Tier 1 Applications: Thick Eager
2. Tier 2 Applications: Thick Lazy
3. Development/Test: Thin Provisioned
4. VDI: Thin Provisioned with linked clones
5. Archive/Backup: Thick Lazy

The choice ultimately depends on your specific requirements for performance, security, storage efficiency, and budget constraints. Consider implementing a tiered approach using different provisioning types for different workload categories to optimize your VMware environment.