diff --git a/.github/actions/start-runner/action.yml b/.github/actions/start-runner/action.yml
index 44a5ff3feb3..17f07ae6324 100644
--- a/.github/actions/start-runner/action.yml
+++ b/.github/actions/start-runner/action.yml
@@ -20,6 +20,9 @@ inputs:
   image-id:
     description: The EC2 image id
     required: true
+  ec2-volume-size:
+    description: Root volume size in GiB (uses the AMI default when omitted)
+    required: false
   security-group-id:
     description: The EC2 security group id
     required: true
@@ -61,6 +64,7 @@ runs:
       with:
         mode: start
         ec2-image-id: ${{ inputs.image-id }}
+        ec2-volume-size: ${{ inputs.ec2-volume-size }}
         ec2-instance-type: ${{ steps.get-ec2-instance-type.outputs.instance-type }}
         subnet-id: ${{ inputs.subnet-id }}
         security-group-id: ${{ inputs.security-group-id }}
diff --git a/.github/workflows/nightly-jsonbench.yaml b/.github/workflows/nightly-jsonbench.yaml
index d5db6f9ba4a..c246ee1f02c 100644
--- a/.github/workflows/nightly-jsonbench.yaml
+++ b/.github/workflows/nightly-jsonbench.yaml
@@ -112,6 +112,8 @@ jobs:
         id: start-linux-runner
         with:
           runner: ${{ vars.LARGE_IOPS_RUNNER }}
+          # Database data, WAL, and compaction files use the root volume.
+          ec2-volume-size: "500"
           aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
           aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
           aws-region: ${{ vars.EC2_RUNNER_REGION }}