VMware Workstation VMs and Disk Caching Explained

A VMware Workstation virtual machine is just a small set of very large files on a host disk. From the host's point of view, every guest operation is a random read or write against those files, which is exactly the workload a disk cache is built for.

This guide explains what the VM files look like, how they behave, and how to size a cache without wasting space.

PAGE CONTENT

• What VMware Stores on Disk
• How VM Disk Files Behave
• How They Interact with a Disk Cache
• Where the Two Conflict
• Configure a Cache for VMware Workstation
• FAQs About VMware and Caching
• Back Up Windows Before You Change Settings

What VMware Stores on Disk

A VM is a handful of files, but each one has a different access pattern:

• The .vmdk files. The virtual disk itself, and by far the largest file in the folder.
• The .vmx file. The configuration, read once at boot and rarely touched afterwards.
• The .nvram file. The virtual BIOS state, tiny and read once at power-on.
• The .lck lock files. Small files written constantly while the VM is running, similar in spirit to database lock files.
• Snapshots. A snapshot adds a delta vmdk that receives every write until the snapshot is removed - see caching for VM snapshots for the details.

How VM Disk Files Behave

The access pattern is the part that matters for caching, and it is not what a file copy looks like:

• Reads and writes are interleaved. A guest OS does both at once, in small blocks, all over the vmdk.
• The working set is much smaller than the file. A 60 GB vmdk might touch only a few gigabytes in a session.
• Boot is read-heavy. The guest reads its own system files, which is a small, repeatable pattern.
• Swap is write-heavy. If the guest pages, the vmdk absorbs random writes that the host cache cannot help - see putting the page file on a RAM disk.
• Snapshots turn writes into a different file. Once a snapshot exists, every write goes to the delta, not the base, which changes what the cache sees.

How They Interact with a Disk Cache

A disk cache sits under VMware's own host cache, and the two layers do different jobs:

• The RAM tier absorbs the hot blocks. Guest memory paging and boot files fit easily and replay on every restart.
• The SSD tier holds the working set. The few gigabytes a VM actually touches in a session fit on a modest tier.
• VMware's host cache is for writes. It coalesces small guest writes, which a disk cache cannot duplicate - the distinction is in write caching vs read caching.
• Boots get faster over time. The same guest system files are read on every boot, which the cache serves from the RAM tier.
• Cold workloads stay cold. A compile or a large copy inside the guest that touches new data will not be served by the cache, as explained in when a disk cache does not help.

Where the Two Conflict

A few setups work against each other, and they are easy to avoid once recognised:

• Keeping snapshots for months. The delta grows until it is larger than the base, and every write goes to the slowest part of the disk.
• Overcommitting VMware memory. When the host swaps guests, the vmdk becomes a swap device, and no cache helps swap.
• Caching the wrong volume. If the vmdk lives on D: and you cache C:, nothing the VM does benefits.
• Putting the vmdk on SMR drives. Shingled drives collapse under sustained random writes - see SMR drives explained.
• Thick-provisioning every VM. A 100 GB flat vmdk takes longer to scan, copy, and cache than a thin one that only holds 10 GB of real data.

Quick summary

A disk cache helps VM boot and steady-state reads. It cannot help guest swap or a snapshot that has grown out of control.

Configure a Cache for VMware Workstation

The cleanest setup is to put the vmdk files on a dedicated volume, point a disk cache at that volume, and size the SSD tier against the working set rather than the full vmdk. Qiling Fast Cache uses a RAM tier for the hottest blocks and an SSD tier for the rest, and shows the hit rate in the task list.

• Free Download
• Windows 11/10/8/7, 100% Secure

Step 1. Install Qiling Fast Cache and open the task list. Make sure no VM is running before configuring the cache.

Step 2. Click the "+" button and select the volume that holds the vmdk files, not the volume that only holds the VMware application itself.

Step 3. Size the SSD tier for the working set of the busiest VM, which is usually a few gigabytes rather than the full vmdk size.

Step 4. Boot the VM a few times, then read the hit rate - see how to check cache hit rate - and confirm that boot files are being served from the faster tier.

FAQs About VMware and Caching

Will a disk cache make my VM boot faster?

Yes, noticeably. Boot reads the same guest system files every time, which is exactly what the RAM tier serves.

Should I cache the VMware application folder?

Little benefit. The application binary is read once at launch and then sits in memory.

Does caching help snapshots?

Only for reads. Snapshot deltas grow with every write, and a cache cannot stop the delta from slowing down.

Should I turn off VMware's own host cache?

No. VMware's host cache coalesces writes, which is a different job from a disk read cache. Keep both.

What about Hyper-V or VirtualBox?

The same rules apply. The guest disk is a host file, and the access pattern is what matters, not the hypervisor brand.

Back Up Windows Before You Change Settings

Reconfiguring storage and cache settings is easier to undo when you have a recent image. Qiling Disk Master creates a full Windows backup you can restore from.

• Free Download
• Windows 11/10/8/7, 100% Secure

Part 1: Create a Full System Backup

Step 1. Install and open Qiling Disk Master. On the home screen, open "Backup and Recovery" and choose "System Backup". This option automatically includes Windows and the hidden boot partitions, so you do not have to select them one by one.

Step 2. Check the source. The disk where Windows is installed and its system partitions are already ticked for you. If you only need your personal documents, run a separate "File Backup" task instead.

Step 3. Click the destination box and choose where the image should be saved. Use an external HDD or SSD, a NAS, or any drive other than the one Windows is installed on, and make sure it has enough free space.

Step 4. Review the task summary and click "Proceed". Wait until the progress bar reaches 100%. Do not unplug the drive or turn off the PC while the backup is running.

Part 2: Restore Windows from the Backup

Step 1. Open Qiling Disk Master again, go to "Backup and Recovery", and select the recovery option. Your backup images are listed, so pick the one you created before the changes began.

Step 2. Choose the target disk or partition. Normally you restore to the original system disk. If the drive was replaced, select the new disk instead, and the restore rebuilds Windows together with its boot partitions.

Step 3. Preview the restore plan, click "Proceed", and confirm the warning. The PC restarts to finish the job, and Windows comes back exactly as it was on the day the image was created.

Conclusion

VMware Workstation is one of the clearest cases for a disk cache. A VM is a small number of large files with a much smaller working set, and the guest boot pattern repeats on every restart. The cache cannot fix guest swap, an overgrown snapshot delta, or a vmdk living on an SMR drive, but for steady-state reads it earns its place. Put the vmdk files on a dedicated volume, point the cache at that volume, size the SSD tier for the working set rather than the full file, and read the hit rate after a few boots instead of guessing.

Protect your PC with Qiling Backup—create a system image before your next round of settings changes.

For more virtualisation and caching guides, see speeding up virtual machines with a disk cache, disk caching for virtual desktops, NTFS compression and caching, how Storage Sense interacts with a cache, and disk caching for Docker and WSL2.

Related Articles

• Hybrid Drives and Software Caching Compared
  Another case where a fast tier sits in front of slow storage.
• Power Loss Protection and Disk Caching
• Thermal Throttling and Disk Caching
• Windows Fast Startup and Disk Caching Explained
• Does a Disk Cache Speed Up File Copies?

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