VMware Thin vs. Thick Provisioning: Types, Advantages, Disadvantages, and Conversion Methods

Optimize the storage of your virtual machines in VMware vSphere by understanding the differences between Thin and Thick Provisioning. Discover the advantages of each type and learn how to convert disks to improve the performance and efficiency of your resources.

Three Disk Modes in VMware vSphere

When creating a virtual machine in VMware vSphere, it is crucial to select the appropriate disk provisioning type. There are three main options:

1. Thick Provisioned Lazy Zeroed
2. Thick Provisioned Eager Zeroed
3. Thin Provision

Each type differs in how disk space is reserved and utilized, impacting both performance and storage resource management.

1. Thick Provisioned Lazy Zeroed

• Description: Immediately reserves all disk space assigned to the virtual machine but only “zeros out” (fills with zeros) the blocks as the VM uses them for the first time.
• Advantages:
  • Ease of management and predictability of used space.
  • Less disk fragmentation.
• Disadvantages:
  • Shorter initial creation time than eager zeroed, but may have slight delays the first time data is written to uninitialized blocks.
  • Less efficient in storage use if not all allocated capacity is utilized.

2. Thick Provisioned Eager Zeroed

• Description: Reserves and “zeros out” all disk blocks at the time of creation.
• Advantages:
  • Better performance in write-intensive operations.
  • Requirement for certain advanced features like VMware Fault Tolerance.
  • The disk is fully initialized from the start, reducing latency in future accesses.
• Disadvantages:
  • Considerably longer initial creation time.
  • Occupies all allocated space from the beginning, even if not used.

3. Thin Provision

• Description: Only occupies the actual space that the virtual machine’s data requires, although the VM “sees” the maximum allocated size. The space expands as the data grows.
• Advantages:
  • Storage optimization: allows overprovisioning and maximizes efficiency.
  • Quick disk creation and lower initial space usage.
• Disadvantages:
  • Risk of overcommitment: if several VMs consume all allocated space, physical storage may run out.
  • May exhibit some fragmentation and performance penalties under high write loads.

Quick Comparison

Summary of Advantages and Disadvantages

• Lazy Zeroed Thick: Simple and predictable, but not efficient in storage if the VM does not use all the space.
• Eager Zeroed Thick: The best performance for critical workloads, but creates disks more slowly and wastes unused space.
• Thin Provision: Maximizes storage usage, but requires monitoring and good management to avoid overloading and performance issues.

How to Convert Disks Between Thin and Thick Provisioning

Sometimes, it may be necessary to convert a disk from one mode to another, whether to gain efficiency, meet requirements, or improve performance.

Converting from Thin to Thick Provisioned (Lazy or Eager Zeroed)

Method 1: vSphere Web Client

1. Power off the virtual machine.
2. Right-click on the VM > Edit Settings.
3. Select the disk to convert and click Expand or use the Convert to Thick option.
4. Choose between Lazy Zeroed or Eager Zeroed based on your needs.
5. Complete the process and power on the VM.

Method 2: Storage vMotion (in appropriately licensed environments)

1. With the VM powered on or off, select Migrate Storage.
2. Select the destination datastore and the disk format change option.
3. Select the desired format (Thin, Lazy Zeroed Thick, Eager Zeroed Thick).
4. Complete the migration: vSphere will automatically convert the disk.

Converting from Thick to Thin Provisioned

1. Power off the virtual machine.
2. Perform a Storage vMotion selecting Thin Provision as the destination format.
3. Alternatively, you can use the vmkfstools utility from the ESXi host: vmkfstools -i original-disk.vmdk -d thin new-disk.vmdk This creates a copy of the disk in thin format.

Conclusions and Recommendations

• Eager Zeroed Thick is the best option for critical workloads and advanced features, though with a higher cost in time and storage.
• Thin Provision is ideal for environments with space limitations or where efficiency is a priority, as long as storage usage is carefully monitored.
• The choice should be tailored to the needs of each environment, balancing performance, costs, and flexibility.

The ability to easily convert disks allows VMware administrators to adjust their storage strategy based on evolving needs.