Types de disques VMware: Mince, Épais et impatient mis à zéro

Understanding VMware Storage

Storage is one of the most important components of any virtual machine. Just like a physical server requires hard drives or SSDs to store operating systems, candidatures, bases de données, and files, VMware virtual machines also require storage resources to function.

VMware provides multiple disk types designed to address different performance, capacity, and management requirements. Administrators can choose between virtual disks stored in datastores or direct access to physical storage devices.

Selecting the correct disk type can significantly impact performance, storage efficiency, évolutivité, and resource utilization.

What Is a VMware Virtual Disk?

A VMware virtual disk is a collection of files that appears to the guest operating system as a standard physical hard drive.

From the perspective of Windows, Linux, or any other operating system installed inside the virtual machine, the virtual disk behaves exactly like a normal storage device.

VMware achieves this abstraction through the use of datastores.

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What Is a Datastore?

A datastore is a storage container used by VMware to hold virtual machine files.

Datastores can reside on:

• Local SSDs
• Local HDDs
• RAID arrays
• SAN storage
• NAS storage
• Fibre Channel storage
• iSCSI storage
• NVMe devices

The datastore hides the underlying storage architecture from the virtual machine and presents a consistent storage interface.

A typical datastore contains:

• Virtual disk files
• VM configuration files
• Instantanés
• Images ISO
• Log files

This design simplifies virtual machine deployment and management.

How VMware Virtual Disks Work

When a virtual machine is created, VMware generates virtual disk files within a datastore.

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These files act as storage containers for the VM.

Par exemple:

Windows Server VM
    │
    └── Virtual Disk (100 GB)
            │
            └── Datastore

The operating system inside the VM sees the virtual disk as a normal hard drive and can:

• Create partitions
• Format filesystems
• Install applications
• Store data

without any awareness of the underlying storage infrastructure.

Dynamic Growth of Virtual Disks

Par défaut, VMware virtual disks do not necessarily consume their full configured size immediately.

Par exemple:

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Configured Disk Size: 100 GB
Actual Data Stored: 20 GB

Depending on the provisioning type, VMware may initially consume only part of the storage and expand as data grows.

This helps optimize storage utilization but can affect performance characteristics.

VMware Virtual Disk Types

These descriptions primarily concern conventional VMDKs on VMFS. NFS, vSAN, storage policies and array thin provisioning can change allocation behavior. Thin disks do not automatically shrink when files are deleted inside a guest; space reclamation needs support and configuration across the storage stack.

VMware provides three primary virtual disk provisioning methods:

• Thick Provision Lazy Zeroed
• Thick Provision Eager Zeroed
• Thin Provision

Each option has different performance and storage characteristics.

Thick Provision Lazy Zeroed

Thick Provision Lazy Zeroed is the default disk format in many VMware deployments.

When this disk type is created:

• The full disk capacity is allocated immediately.
• Blocks are not zeroed during creation.
• Blocks are zeroed when first written by the virtual machine.

Par exemple:

Virtual Disk Size: 100 GB
Datastore Usage: 100 GB
Data Stored in VM: 5 GB

The datastore still reserves the entire 100 GB from the moment the disk is created.

Avantages

• Faster creation compared to eager zeroed disks
• Predictable storage allocation
• Good overall performance

Inconvénients

• Consumes full allocated space immediately
• Slight performance overhead during first write operations

Understanding Disk Zeroing

Zeroing is the process of writing zeros to storage blocks.

Exemple:

000000000000000000

This ensures blocks are initialized before use.

Zeroing helps improve storage consistency and supports advanced VMware features.

Thick Provision Eager Zeroed

Thick Provision Eager Zeroed allocates and zeroes the entire disk during creation.

Par exemple:

Virtual Disk Size: 100 GB
Datastore Usage: 100 GB

Unlike lazy zeroed disks, all storage blocks are prepared before the VM uses them.

Avantages

• Avoids first-write zeroing overhead
• No runtime zeroing overhead
• Required for certain VMware features

Inconvénients

• Longer disk creation time
• Full storage allocation immediately

When to Use Eager Zeroed Disks

Eager Zeroed disks are commonly recommended for:

• High-performance databases
• Enterprise applications
• VMware Fault Tolerance
• Latency-sensitive workloads

Because all blocks are prepared in advance, performance remains consistent during operation.

Thin Provision

Thin Provisioning allocates storage only when data is actually written.

Exemple:

Configured Disk Size: 100 GB
Stored Data: 15 GB
Datastore Usage: 15 GB

The virtual disk grows dynamically as additional data is written.

Avantages

• Efficient storage utilization
• Reduced initial storage consumption
• Increased flexibility

Inconvénients

• Possible allocation and first-write overhead
• Potential datastore overcommitment
• Requires capacity monitoring

Thin Provisioning Example

Assume a datastore contains:

Datastore Capacity: 1 TB

You create ten virtual machines:

10 × 200 GB Virtual Disks

Total configured storage:

2 TB

Although only 1 TB physically exists, thin provisioning allows this because not all virtual machines are expected to consume their full allocation immediately.

This technique is called storage overcommitment.

Administrators must monitor datastore utilization carefully to prevent capacity exhaustion.

Comparing VMware Virtual Disk Types

Raw Disks, RDM and Passthrough

Physical-disk access is product-specific. vSphere Raw Device Mapping uses a mapping file to expose a supported storage LUN; it is different from passing through an entire storage controller and from raw-disk features in desktop VMware products. Do not assume local disks, instantanés, vMotion or backup APIs behave the same across these options.

Choose raw access only for a documented application or storage requirement. Check the exact product, storage and backup support matrix first. Giving multiple ordinary filesystems write access to the same disk can corrupt data; shared block storage needs a cluster-aware filesystem or application design. Use SMB or NFS for normal file sharing.

Choosing the Right VMware Disk Type

Selecting the correct disk type depends on workload requirements.

Choose Thick Provision Lazy Zeroed When

• General-purpose virtual machines
• Predictable storage allocation
• Balanced performance and capacity management

Choose Thick Provision Eager Zeroed When

• The workload benefits from avoiding first-write allocation
• A verified feature requirement calls for eager-zeroed disks
• High-transaction workloads are deployed

Choose Thin Provision When

• Storage efficiency is a priority
• Large environments require flexible capacity allocation
• Datastore utilization is monitored closely

Choose Physical Disks When

• Specialized storage access is required
• Existing operating systems must be used
• Specific high-performance workloads justify direct disk access

Storage Planning Best Practices

When deploying VMware environments:

• Monitor datastore usage regularly
• Avoid excessive storage overcommitment
• Choose disk provisioning from workload measurements and feature requirements
• Maintain storage redundancy
• Implement backup strategies
• Test recovery procedures
• Separate production and backup storage

Storage architecture plays a major role in virtualization performance and reliability.

Understanding VMware Storage Options

VMware provides a flexible storage platform capable of supporting everything from small test environments to large enterprise infrastructures. Virtual disks simplify deployment and management while offering multiple provisioning methods to balance performance and storage efficiency.

Whether using Thick Provision Lazy Zeroed, Thick Provision Eager Zeroed, Thin Provision, or direct physical disk access, understanding how each storage type works allows administrators to design VMware environments that meet both performance goals and operational requirements.