VMware virtual machines (VMs) function like physical servers. The hard disk space is where the operating system (OS), applications, files, and other information lives. However, VMware virtual disks have storage options beyond that of physical servers.
In most cases, configurations for your VMware VMs have virtual hard disks for your storage needs. However, on some occasions, your VMs may need access to the physical hard disks on the host servers.
Let’s look at the VMware disk types and how they work.
What is a Virtual Disk in VMware?
A virtual disk is a set of files appearing as a physical disk drive to a VM's operating system. VMware makes the files appear to the OS this way through its use of datastores. These file storage containers are either local to the host server or remotely located across a network on another device, such as a storage area network (SAN).
The datastores mask the specifics of the storage devices used and provide a standard for storing VM files. When configuring a VM with a virtual disk, a new OS gets installed without repartitioning a physical disk or rebooting the host server.
Depending on the virtual disk size and the host OS, VMware creates files to hold the virtual disks. By default, the virtual disk files start small and grow to the max needed.
The advantage is that the smaller file size requires less storage space and is easier to move if you relocate VMs to a new location. The disadvantage is that writing data to a disk configured in this way takes longer.
What are the Different Types of Virtual Disks?
When using VMware and vSphere, there are three main virtual hard disk types:
- Thick Provision Lazy Zeroed
- Thick Provision Eager Zeroed
- Thin Provision
We will take a closer look at each of these VMware disk types.
Virtual Hard Disk Types
Thick Provision Lazy Zeroed
Thick Provision Lazy Zeroed is the default disk type. During creation, the space required for the virtual disk gets allocated. It is zeroed on command with the first write from the VM. Thus, a virtual disk set up as 10 GB will use 10 GB on the datastore, despite the actual usage in the VM's OS.
Thick Provision Eager Zeroed
Thick Provision Eager Zeroed also sees its virtual disk space allocated during the disk creation. Like thick provisioned lazy zeroed, space is zeroed upon disk creation. While this type of disk takes the longest to create, there is an increase in performance since zeroing does not happen at runtime. It also has a virtual disk set up as 10 GB using 10 GB on the datastore, despite the actual usage in the VM's OS. Advanced vSphere features like fault tolerance require using this disk type.
Thin Provision uses only the space needed on the datastore. In other words, setting up a 10 GB virtual disk and putting 3 GB of data on it will result in 3 GB of space used on the datastore. Although the size increases as required, it will not shrink when deleting files in the VM OS. As a result, thin provisioned disks have the lowest performance of the three VMware disk types.
What is a Physical Disk in VMware?
A physical disk in VMware is the direct access of the host server’s physical hard drive or partition. Customers will use physical disks if they want VMware to run an OS from an existing disk partition. Also, a great use case would be workloads needing higher input/output operations per second (IOPS) performance, like virtual desktop infrastructure (VDI) and data archiving solutions.
One thing to note is that it would be best not to use physical disks to share files between the host server and VM OSs. Due to potential data corruption, it is not safe for the same partition to be visible to both the host server and VMs. Instead, shared folders are the better solution.
There are several options when setting up VMware disks. Whether you want to use the physical host server disks or one of the virtual options for your VM disks will depend on your specific needs.
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