Enhancing VMware Performance with PCI Passthrough
When a customer came to us with a sluggish VMware setup, the issue was simple but frustrating: performance just wasn’t where it needed to be. File transfers were slow, processes lagged, and it was starting to affect day-to-day work.
Their baseline speed sat at around 43 MB/s – fine on paper, but not in practice. After some investigation, we implemented PCI passthrough, and the result was a jump to 207 MB/s. Here’s how we got there.
What’s Going On Under the Hood?
VMware allows multiple virtual machines to share the same physical hardware. Normally, those machines access hardware through a virtual layer, which adds flexibility but also overhead.
PCI passthrough changes that. Instead of going through the virtual layer, a virtual machine gets direct access to a physical device – like a network card or storage controller. Less abstraction, less overhead, better performance.
The Problem
In this case, the customer was relying on virtualised storage and network access. It worked, but not efficiently. The system had grown over time, and what started as a tidy setup had become a bottleneck.
Standard tweaks – resource allocation, tuning settings – only went so far. The underlying issue was the virtualisation layer itself.
The Fix: PCI Passthrough
We started by checking hardware compatibility. Not every setup supports passthrough, so this step matters.
Once confirmed, we:
- Identified the right PCI device to pass through
- Reserved it for exclusive use
- Configured VMware to allow direct access from the virtual machine
It’s not a complicated process, but it does need care—especially to avoid conflicts or losing access to critical hardware.
The Result
The difference was immediate:
- Before: 43 MB/s
- After: 207 MB/s
Beyond the numbers, the system simply felt faster. Tasks completed quicker, delays disappeared, and the setup became far more usable day-to-day.
When Does This Make Sense?
PCI passthrough isn’t always the answer. You lose some flexibility – live migration and certain failover features may no longer work as expected.
But it’s worth considering if:
- You’ve got performance-critical workloads
- You’re hitting limits with virtualised I/O
- You need predictable, consistent speed
Final Thoughts
This wasn’t about throwing more resources at the problem – it was about removing a bottleneck. In the right situation, PCI passthrough can make a dramatic difference with relatively little change.
If you’re dealing with a VMware setup that feels slower than it should, it’s often worth stepping back and asking: is the virtual layer helping, or getting in the way?