Following on from my last post about Getting Started With KubeVirt & SQL Server, in this post I want to see if I can improve the performance from the initial test I ran.
In the previous test, I used SQL Server 2025 RC1…so wanted to change that to RTM (now that’s it’s been released) but I was getting some strange issues running in the StatefulSet. However, SQL Server 2022 seemed to have no issues and as much as I want to investigate what’s going on with 2025 (pretty sure it’s host based, not an issue with SQL 2025)…I want to dive into KubeVirt more…so let’s go with 2022 in both KubeVirt and the StatefulSet.
I also separated out the system databases, user database data, and user database log files onto separate volumes…here’s what the StatefulSet manifest looks like: –
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mssql-statefulset
spec:
serviceName: "mssql"
replicas: 1
podManagementPolicy: Parallel
selector:
matchLabels:
name: mssql-pod
template:
metadata:
labels:
name: mssql-pod
annotations:
stork.libopenstorage.org/disableHyperconvergence: "true"
spec:
securityContext:
fsGroup: 10001
containers:
- name: mssql-container
image: mcr.microsoft.com/mssql/rhel/server:2022-CU22-rhel-9.1
ports:
- containerPort: 1433
name: mssql-port
env:
- name: MSSQL_PID
value: "Developer"
- name: ACCEPT_EULA
value: "Y"
- name: MSSQL_AGENT_ENABLED
value: "1"
- name: MSSQL_SA_PASSWORD
value: "Testing1122"
- name: MSSQL_DATA_DIR
value: "/opt/sqlserver/data"
- name: MSSQL_LOG_DIR
value: "/opt/sqlserver/log"
resources:
requests:
memory: "8192Mi"
cpu: "4000m"
limits:
memory: "8192Mi"
cpu: "4000m"
volumeMounts:
- name: sqlsystem
mountPath: /var/opt/mssql/
- name: sqldata
mountPath: /opt/sqlserver/data/
- name: sqllog
mountPath: /opt/sqlserver/log/
volumeClaimTemplates:
- metadata:
name: sqlsystem
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 10Gi
storageClassName: px-fa-direct-access
- metadata:
name: sqldata
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 50Gi
storageClassName: px-fa-direct-access
- metadata:
name: sqllog
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 25Gi
storageClassName: px-fa-direct-access
And here’s what the KubeVirt VM manifest looks like: –
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
name: win2025
spec:
runStrategy: Manual # VM will not start automatically
template:
metadata:
labels:
app: sqlserver
spec:
domain:
firmware:
bootloader:
efi:
secureBoot: false
resources: # requesting same limits and requests for guaranteed QoS
requests:
memory: "8Gi"
cpu: "4"
limits:
memory: "8Gi"
cpu: "4"
devices:
disks:
# Disk 1: OS
- name: osdisk
disk:
bus: scsi
# Disk 2: SQL System
- name: sqlsystem
disk:
bus: scsi
# Disk 3: SQL Data
- name: sqldata
disk:
bus: scsi
# Disk 4: SQL Log
- name: sqllog
disk:
bus: scsi
# Windows installer ISO
- name: cdrom-win2025
cdrom:
bus: sata
readonly: true
# VirtIO drivers ISO
- name: virtio-drivers
cdrom:
bus: sata
readonly: true
# SQL Server installer ISO
- name: sql2022-iso
cdrom:
bus: sata
readonly: true
interfaces:
- name: default
model: virtio
bridge: {}
ports:
- port: 3389 # port for RDP
- port: 1433 # port for SQL Server
networks:
- name: default
pod: {}
volumes:
- name: osdisk
persistentVolumeClaim:
claimName: winos
- name: sqlsystem
persistentVolumeClaim:
claimName: sqlsystem
- name: sqldata
persistentVolumeClaim:
claimName: sqldata
- name: sqllog
persistentVolumeClaim:
claimName: sqllog
- name: cdrom-win2025
persistentVolumeClaim:
claimName: win2025-pvc
- name: virtio-drivers
containerDisk:
image: kubevirt/virtio-container-disk
- name: sql2022-iso
persistentVolumeClaim:
claimName: sql2022-pvc
I then ran the hammerdb test again…running for 10 minutes with a 2 minute ramp up time. Here are the results: –
# Statefulset result TEST RESULT : System achieved 46594 NOPM from 108126 SQL Server TPM # KubeVirt result TEST RESULT : System achieved 18029 NOPM from 41620 SQL Server TPM
Oooooook…that has made a difference! KubeVirt TPM is now up to 38% of the statefulset TPM. But I’m still seeing a high privileged CPU time in the KubeVirt VM: –
So I went through the docs and found that there are a whole bunch of options for VM configuration…the first one I tried was the Hyper-V feature. This should allow Windows to use paravirtualized interfaces instead of emulated hardware, reducing VM exit overhead and improving interrupt, timer, and CPU coordination performance.
Here’s what I added to the VM manifest: –
features:
hyperv: {} # turns on Hyper-V feature so the guest “thinks” it’s running under Hyper-V - needs the Hyper-V clock timer too, otherwise VM pod will not start
clock:
timer:
hyperv: {}
N.B. – for more information on what’s happening here, check out this link: –
https://www.qemu.org/docs/master/system/i386/hyperv.html
Stopped/started the VM and then ran the test again. Here’s the results: –
TEST RESULT : System achieved 40591 NOPM from 94406 SQL Server TPM
Wait, what!? That made a huge difference…it’s now 87% of the StatefulSet result! AND the privileged CPU time has come down: –
But let’s not stop there…let’s keep going and see if we can get TPM parity between KubeVirt and SQL in a StatefulSet.
There’s a bunch more flags that can be set for the Hyper-V feature and the overall VM, so let’s set some of those: –
features:
acpi: {} # ACPI support (power management, shutdown, reboot, device enumeration)
apic: {} # Advanced Programmable Interrupt Controller (modern interrupt handling for Windows/SQL)
hyperv: # turns on Hyper-V vendor feature block so the guest “thinks” it’s running under Hyper-V. - needs the Hyper-V clock timer too, otherwise VM pod will not start
reenlightenment: {} # Allows guest to update its TSC frequency after migrations or time adjustments
ipi: {} # Hyper-V IPI acceleration - faster inter-processor interrupts between vCPUs
synic: {} # Hyper-V Synthetic Interrupt Controller - improves interrupt delivery
synictimer: {} # Hyper-V synthetic timer - stable high-resolution guest time source
spinlocks:
spinlocks: 8191 # Prevents Windows spinlock stalls on SMP systems - avoids boot/timeouts under load
reset: {} # Hyper-V reset infrastructure - cleaner VM resets
relaxed: {} # Relaxed timing - reduces overhead when timing deviations occur under virtualization
vpindex: {} # Per-vCPU indexing - improves Windows scheduler awareness of vCPU layout
runtime: {} # Hyper-V runtime page support - gives guest better insight into hypervisor behavior
tlbflush: {} # Hyper-V accelerated TLB flush - improves scalability on multi-vCPU workloads
frequencies: {} # Exposes host CPU frequency data - allows proper scaling & guest timing
vapic: {} # Virtual APIC support - reduces interrupt latency and overhead
clock:
timer:
hyperv: {} # Hyper-V clock/timer - stable time source, recommended when using Hyper-V enlightenments
And now, what’s the TPM we’re getting with hammerdb…
TEST RESULT : System achieved 40483 NOPM from 94051 SQL Server TPM
Ha ha! Nearly there…so what else can we do?
Memory and CPU wise…I went and added: –
ioThreadsPolicy: auto # Automatically allocate IO threads for QEMU to reduce disk I/O contention
cpu:
cores: 4
dedicatedCpuPlacement: true # Guarantees pinned physical CPUs for this VM to improve latency & stability
isolateEmulatorThread: true # Pins QEMU’s emulator thread to a dedicated pCPU instead of sharing with vCPUs
model: host-passthrough # Exposes all host CPU features directly to the VM
numa:
guestMappingPassthrough: {} # Mirrors host NUMA topology to the guest to reduce cross-node latency
memory:
hugepages:
pageSize: 1Gi # Uses 1Gi hugepages for reduced TLB pressure
N.B. – this required configuring the host to reserve hugepages at boot
And then for disks…I installed the latest virtio drivers on the VM…switched the disks for the SQL system, data, and log files to use virtio instead of a scsi bus and then added for each disk: –
dedicatedIOThread: true
Other device settings added were: –
autoattachGraphicsDevice: false # Do not attach a virtual graphics/display device (VNC/SPICE) - removes unnecessary emulation autoattachMemBalloon: false # Disable the VirtIO memory balloon - prevents dynamic memory changes, improves consistency autoattachSerialConsole: true # Attach a serial console for debugging and virtctl console access networkInterfaceMultiqueue: true # Enable multi-queue virtio-net so NIC traffic can use multiple RX/TX queues
All of this results in a bit of a monster manifest file for the VM: –
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
name: win2025
spec:
runStrategy: Manual # VM will not start automatically
template:
metadata:
labels:
app: sqlserver
spec:
domain:
ioThreadsPolicy: auto # Automatically allocate IO threads for QEMU to reduce disk I/O contention
cpu:
cores: 4
dedicatedCpuPlacement: true # Guarantees pinned physical CPUs for this VM - improves latency & stability
isolateEmulatorThread: true # Pins QEMU’s emulator thread to a dedicated pCPU instead of sharing with vCPUs
model: host-passthrough # Exposes host CPU features directly to the VM - best performance (but less portable)
numa:
guestMappingPassthrough: {} # Mirrors host NUMA topology to the guest - reduces cross-node memory latency
memory:
hugepages:
pageSize: 1Gi # Uses 1Gi hugepages for reduced TLB pressure - better performance for large-memory SQL
firmware:
bootloader:
efi:
secureBoot: false # Disable Secure Boot (often required when using custom/older virtio drivers)
features:
acpi: {} # ACPI support (power management, shutdown, reboot, device enumeration)
apic: {} # Advanced Programmable Interrupt Controller (modern interrupt handling for Windows/SQL)
hyperv: # Enable Hyper-V enlightenment features for Windows guests to improve performance & timing
reenlightenment: {} # Allows guest to update its TSC frequency after migrations or time adjustments
ipi: {} # Hyper-V IPI acceleration - faster inter-processor interrupts between vCPUs
synic: {} # Hyper-V Synthetic Interrupt Controller - improves interrupt delivery
synictimer: {} # Hyper-V synthetic timer - stable high-resolution guest time source
spinlocks:
spinlocks: 8191 # Prevents Windows spinlock stalls on SMP systems - avoids boot/timeouts under load
reset: {} # Hyper-V reset infrastructure - cleaner VM resets
relaxed: {} # Relaxed timing - reduces overhead when timing deviations occur under virtualization
vpindex: {} # Per-vCPU indexing - improves Windows scheduler awareness of vCPU layout
runtime: {} # Hyper-V runtime page support - gives guest better insight into hypervisor behavior
tlbflush: {} # Hyper-V accelerated TLB flush - improves scalability on multi-vCPU workloads
frequencies: {} # Exposes host CPU frequency data - allows proper scaling & guest timing
vapic: {} # Virtual APIC support - reduces interrupt latency and overhead
clock:
timer:
hyperv: {} # Hyper-V clock/timer - stable time source, recommended when using Hyper-V enlightenments
resources: # requests == limits for guaranteed QoS (exclusive CPU & memory reservation)
requests:
memory: "8Gi"
cpu: "4"
hugepages-1Gi: "8Gi"
limits:
memory: "8Gi"
cpu: "4"
hugepages-1Gi: "8Gi"
devices:
autoattachGraphicsDevice: false # Do not attach a virtual graphics/display device (VNC/SPICE) - removes unnecessary emulation
autoattachMemBalloon: false # Disable the VirtIO memory balloon - prevents dynamic memory changes, improves consistency
autoattachSerialConsole: true # Attach a serial console for debugging and virtctl console access
networkInterfaceMultiqueue: true # Enable multi-queue virtio-net so NIC traffic can use multiple RX/TX queues
disks:
# Disk 1: OS
- name: osdisk
disk:
bus: scsi # Keep OS disk on SCSI - simpler boot path once VirtIO storage is already in place
cache: none
# Disk 2: SQL System
- name: sqlsystem
disk:
bus: virtio
cache: none
dedicatedIOThread: true # Give this disk its own IO thread - reduces contention with other disks
# Disk 3: SQL Data
- name: sqldata
disk:
bus: virtio
cache: none
dedicatedIOThread: true # Separate IO thread for data file I/O - improves parallelism under load
# Disk 4: SQL Log
- name: sqllog
disk:
bus: virtio
cache: none
dedicatedIOThread: true # Separate IO thread for log writes - helps with low-latency sequential I/O
# Windows installer ISO
- name: cdrom-win2025
cdrom:
bus: sata
readonly: true
# VirtIO drivers ISO
- name: virtio-drivers
cdrom:
bus: sata
readonly: true
# SQL Server installer ISO
- name: sql2022-iso
cdrom:
bus: sata
readonly: true
interfaces:
- name: default
model: virtio # High-performance paravirtualized NIC (requires NetKVM driver in the guest)
bridge: {} # Bridge mode - VM gets an IP on the pod network (via the pod’s primary interface)
ports:
- port: 3389 # RDP
- port: 1433 # SQL Server
networks:
- name: default
pod: {} # Attach VM to the default Kubernetes pod network
volumes:
- name: osdisk
persistentVolumeClaim:
claimName: winos
- name: sqlsystem
persistentVolumeClaim:
claimName: sqlsystem
- name: sqldata
persistentVolumeClaim:
claimName: sqldata
- name: sqllog
persistentVolumeClaim:
claimName: sqllog
- name: cdrom-win2025
persistentVolumeClaim:
claimName: win2025-pvc
- name: virtio-drivers
containerDisk:
image: kubevirt/virtio-container-disk
- name: sql2022-iso
persistentVolumeClaim:
claimName: sql2022-pvc
And then I ran the tests again: –
# StatefulSet TEST RESULT : System achieved 47200 NOPM from 109554 SQL Server TPM # KubeVirt TEST RESULT : System achieved 46563 NOPM from 108184 SQL Server TPM
BOOOOOOOOOM! OK, so that’s 98% of the TPM achieved in the StatefulSet. And there’s a bit of variance in those results so these are now pretty much the same!
Ok so it’s not the most robust performance testing ever done…and I am fully aware that testing in a lab like this is one thing, whereas running SQL Server in KubeVirt…even in a dev/test environment is a completely other situation. There are still questions over stability and resiliency BUT from this I hope that it shows that we shouldn’t be counting KubeVirt out as a platform for SQL Server, based on performance.
Thanks for reading!