# Azure Batch + Nextflow: Cannot exceed vCPU concurrency even with fractional cpus — is CPU oversubscription impossible?
**URL:** https://community.seqera.io/t/azure-batch-nextflow-cannot-exceed-vcpu-concurrency-even-with-fractional-cpus-is-cpu-oversubscription-impossible/2680
**Category:** Ask for help
**Tags:** nextflow, azure, azure-batch
**Created:** [May 19, 2026, 9:15am UTC](https://community.seqera.io/t/azure-batch-nextflow-cannot-exceed-vcpu-concurrency-even-with-fractional-cpus-is-cpu-oversubscription-impossible/2680 "2026-05-19T09:15:14Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mantczakaus](https://community.seqera.io/u/mantczakaus)
#### Post date: [May 19, 2026, 9:15am UTC](https://community.seqera.io/t/azure-batch-nextflow-cannot-exceed-vcpu-concurrency-even-with-fractional-cpus-is-cpu-oversubscription-impossible/2680/1 "2026-05-19T09:15:14Z")
Hi, I’m running Nextflow on Azure Batch using Standard\_L8as\_v3 nodes (8 vCPUs). Azure Batch allows `taskSlotsPerNode` to be set higher than the vCPU count (e.g., 16), but Nextflow throws this error if I try:
```auto
Azure Batch pool 'X' slots per node does not match the VM num cores (slots: 16, cores: 8)
```
So I’m forced to keep `taskSlotsPerNode = 8`.
My processes only require `cpus = 0.5`, so in theory Nextflow should be able to schedule 16 tasks per node. However, Azure Batch still limits me to 8 concurrent tasks, because `taskSlotsPerNode` is capped at 8 and Nextflow won’t allow increasing it.
This means I can’t use fractional CPUs to increase concurrency, and I end up paying for unused CPU capacity.
Is there any supported way to run more tasks per node than the vCPU count (i.e., oversubscribe CPUs), or is batching tasks the only workaround?
---
### Author:  [@ewels](https://community.seqera.io/u/ewels)
#### Post date: [May 19, 2026, 3:48pm UTC](https://community.seqera.io/t/azure-batch-nextflow-cannot-exceed-vcpu-concurrency-even-with-fractional-cpus-is-cpu-oversubscription-impossible/2680/2 "2026-05-19T15:48:18Z")
Hi @mantczakaus,
I’m afraid that this isn’t possible currently, though it’s the kind of thing that we might be able to support in the future. If you fancy creating an issue on the Nextflow GitHub repo with your suggestion, that would be great!
Phil
---
### Author:  [@system](https://community.seqera.io/u/system)
#### Post date: [May 26, 2026, 3:48pm UTC](https://community.seqera.io/t/azure-batch-nextflow-cannot-exceed-vcpu-concurrency-even-with-fractional-cpus-is-cpu-oversubscription-impossible/2680/3 "2026-05-26T15:48:44Z")
This topic was automatically closed 7 days after the last reply. New replies are no longer allowed.