Effects of CPU topology on sqlserver guests with AHV.

Posted on February 28, 2023February 28, 2023 by gary

VM CPU Topology

The topology (layout) that AHV presents virtual Sockets/CPU to the guest operating system will usually be different than the physical topology. This is expected because we typically present a subset of all cores to the guest VMs.

Usually it is the total number of vCPU given to the VM that matters, not the specific topology, but in the case of SQLserver running an analytical workload (a TPC-H like workload from HammerDB) the topology passed to the VM does make a difference. Between 10% and 20% when measured by the total runtime.

[I think that the reason we see a difference here is that (a) the analytical workloads use hardly any storage bandwidth (I sized the database to fit in memory) and (b) there is probably a lot of cross-talk between the cores/memory as the DB engine issues parallel queries.]

At any rate we see that passing 20 cores as “20 sockets of 1 core” beats the performance of “1 socket with 20 cores” by a wide margin. The physical topology is two sockets of 20 cores on each socket. Thankfully the better performing option is the default.

CPU Topology may make a difference for SQL server running analytical workloads.

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Using cloud-init with AHV command line

Posted on August 26, 2022September 7, 2022 by gary

TL;DR

Using cloud-init with AHV is conceptually identical to using KVM/QEMU- we need to use a few different tools with AHV
You will need a Linux image that is configured to use cloud-init. A good source is cloud-images.ubuntu.com
We will create a cloud-init textual file and create a mountable version using the cloud-localds tool on a Linux host
We will attach the cloud-init enabled ubuntu image and our cloud-init customization file to the VM at boot time
At boottime ubuntu will access the cloud-init data mounted as a CDROM and do the customization for us

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AHV Tip: Shutdown multiple VMs in parallel

Posted on May 6, 2022September 7, 2022 by gary

Often in my lab I want to shutdown a large number of VMs quickly. In the example below I submit the power-off command for a maximum of 50 VMs in parallel. Be aware that we’re using the command line, and in line with true Unix philosophy the OS will assume we know what we are doing and obey us completely and immediately. In other words pasting the below commands to your CVM will immediately shutdown all powered on VMs.

 for i in $(acli  vm.list power_state=on | awk '{ print $(NF) }' |tail -50); do acli vm.off $i &  done

Install a bitnami image to Nutanix AHV cluster.

Posted on June 28, 2019June 28, 2019 by gary

One of the nice things about using public cloud is the ability to use pre-canned application virtual appliances created by companies like Bitnami.

We can use these same appliance images on Nutanix AHV to easily do a Postgres database benchmark

Step 1. Get the bitnami image

wget  https://bitnami.com/redirect/to/587231/bitnami-postgresql-11.3-0-r56-linux-debian-9-x86_64.zip

Step 2. Unzip the file and convert the bitnami vmdk images to a single qcow2[1] file.

qemu-img convert *vmdk bitnami.qcow2

Put the bitnami.qcow2 image somewhere accessible to a browser, connected to the Prism service, then upload using the “Image Configuration”

Once the image is uploaded, it’s time to create a new VM based on that image

Once booted, you’ll see the bitnami logo and you can configure the bitnami passwords, enable ssh etc. using the console.

Enable/disable ssh in bitnami images
Connecting to Postgres in bitnami images
Note – when you “sudo -c postgres <some-psql-tool> the password it is asking for is the Postgres DB password (stored in ./bitnami-credentials) not any unix user password.

Once connected to the appliance we can use postgres and pgbench to generate simplistic database workload.

[1] Do this on a Linux box somewhere. For some reason the conversion failed using my qemu utilities installed via brew. Importing OVAs direct into AHV should be available in the future.

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