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Best practices in virtualized environments

(PowerKVM)

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Picture

Breno Leitao

Advisory Software Engineer brenohl@br.ibm.com

© 2014 IBM Corporation

Introduction

Learn best practices on Kernel-based Virtual Machine.

Agenda:

Command line management

Storage

Network

CPU

Snapshots

General tips

© 2014 IBM Corporation ● Systems Technical University ● 28 – 30 October | Atibaia, Sao Paulo, Brazil

Terminology


General Understanding

IBM PowerKVM is the KVM ported to IBM POWER processors.


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General Understanding

IBM PowerKVM management screen (GUI)


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Command line

Using command line provides you more control over you environment.

Images and other files are at /var/lib/libvirt



Network



Storage

Every configuration is an XML file

# virsh edit/dump-xml


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Command line: How to handle the VM more properly

Examples:

• Create amount of disk

– # qemu-img create -f qcow2 /var/lib/libvirt/images/ubuntu.qcow2

50G

– # virsh vol-create-as disks ubuntu 50G --format qcow2

• Virt-install:

– # virt-install --name=ubuntu1410 --cdrom=/root/utopic-serverppc64el.iso --memory=4096 --disk 10G --network=default

• Keep the machine up after a reboot

– #virsh autostart <VM name>

• Edit VM configuration:

– # virsh edit <VM name>

• Log into the console:

– # virsh console <VM name>


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Storage (Disk)

Use Logical disk for performance.

Use File system images for storage virtualization.

Many other types of pool:



NFS

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SCSI



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ISCSI

ZFS VM File system

VM Image

Hypervisor File system

Hypervisor Disk

VM FS

VM Disk

Hypervisor Disk


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Storage (Images)

Qcow2

– Copy on Write file format.

– Supports backing file:

• Have a base file and all changes on the base files are written in a different file.

– Usually small than raw format

– Create snapshot

Raw

– File system as a file

– Can be mounted as a file system

– The image file will be as big as the VM file system

You can convert from one type to another using qemu-image too.

$ virsh vol-create-as disks qcow_image 10G --format qcow2

Vol qcow_image created

$ virsh vol-create-as disks raw 10G --format raw

Vol raw created

$ ls /tmp/pool/qcow_image -lah

-rw------- 1 brenohl brenohl 193K Oct 28 11:13

/tmp/pool/qcow_image

QCOW2

$ ls /tmp/pool/raw -lah

-rw------- 1 brenohl brenohl 10G Oct 28 11:15 /tmp/pool/raw


RAW

Network Storage


Networking

Interfaces

All the host network interfaces are managed by virsh.

Easily create or assign NIC to a guest.

Create and handle bridges.

Network transactions and network commits.

Net

Used to create bridges automatically

Many type of network pools.



Isolated













Forward

NAT

Bridged

Route

Passthrough hostdev

<network>

<name>nat_pool</name>

<uuid>11f69826-6dec-47fc-ae46-efa0f9b714f4</uuid>

<forward mode='nat'/>

<bridge name='virbr1' stp='on' delay='0'/>

<mac address='52:52:00:d1:19:b5'/>

<ip address='192.168.22.1' netmask='255.255.255.0'>

<dhcp>

<range start='192.168.22.2' end='192.168.22.254'/>

</dhcp>

</ip>

</network>


Networking

Bridging is usually the best way to configure your network if you are not able to passthrough.

# virsh net-info default

Name default

UUID 11f69826-6de

Active: yes

Persistent: yes

Autostart: yes

Bridge: virbr1


Snapshots

Always use snapshot when you reach a point you want to 'save'. You run the snapshot command live:



No Downtime at saving or backing up.





Very fast and easy to be done

Demo how to create a snapshot and how to recover it.

$ virsh help snapshot

Snapshot (help keyword 'snapshot'): snapshot-create Create a snapshot from XML snapshot-create-as Create a snapshot from a set of args snapshot-current Get or set the current snapshot snapshot-delete Delete a domain snapshot snapshot-dumpxml Dump XML for a domain snapshot snapshotedit edit XML for a snapshot snapshotinfo snapshotlist snapshot information

List snapshots for a domain snapshot-parent Get the name of the parent of a snapshot snapshot-revert Revert a domain to a snapshot

$ virsh help snapshot-list


Creating snapshot


Reverting snapshot


VirtIO

The VirtIO API is a high performance API that para-virtualized devices use to gain speed and efficiency.









Virtio-scsi

Virtio-blk

Virtio-console

Virtio_net

The guest OS needs to have the drivers installed:

At the moment, only Ubuntu versions have them.


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CPU overcommitment



Guest usually does not run on 100% of the CPU all the time



CPUs run in burst mode



CPU overcommitment is usually a good thing to do.



The overcommitment rate depends on the workload, but usually 20-50% of overcommitment is a good number

Best practice: Target system use at 80% or lower


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CPU Micro Threading

Versus


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Enabling CPU Micro Threading

1) Ensure that all guests are not running.

2) Set the number of subcores to 1:

# ppc64_cpu --subcores-per-core=1

3) Enable SMT on the host:

# ppc64_cpu --smt=on

4) Set the number of subcores to 4:

# ppc64_cpu --subcores-per-core=4

5) Turn the SMT off on the host:

# ppc64_smt --smt=off


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CPU Pinning



CPU pinning allows a guest virtual machine to be pinned to a given CPU or set of

CPUs. It means that the hypervisor will schedule only vCPUs in those CPUs that the guest is pinned to. By default, the guest can be scheduled on any CPU.

<vcpu placement=’static’ cpuset=’0,8’>8</vcpu>

CPU Sharing





CPU sharing defines the amount of CPU time a VM will have

Usually a VM has sharing time of 1024. If your VM is configured to have 2048, it is going to have twice the CPU time compared to a default VM in an overcommitment scenario.

<cputune>

<shares>256</shares>

</cputune>


Kernel Same page Merge (KSM)

KSM is a kernel feature in KVM that shares memory pages between various processes, over-committing the memory.

How to enable:

# systemctl start ksmtuned

Monitoring:

# cat /sys/kernel/mm/ksm/page_shared

# cat /sys/kernel/mm/ksm/page_sharing

# cat /sys/kernel/mm/ksm/sleep_milisecs

# cat /sys/kernel/mm/ksm/full_scans

If you configure KSM to act too aggressively, KSM might use an entire processor thread.


Huge Pages

The bigger pages (huge page) you have in the hypervisor, the less page your system needs, turning the memory management easier when looking for contiguous memory.

Configuration:

<memoryBacking>

<hugepages/>

</memoryBacking>

Memory balloning

Memory ballooning is a technique that allows the guest memory to be increased or decreased cooperatively, depending on the amount of free memory available on the guests and hypervisor.

Configuration

<memballoon model=’ virtio’>


Memory ballooning demo


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Network Time Protocol (NTP)

Set the same time on guest and hypervisor.


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Disk Hot Plug

Attaching disks to the virtual machine

On the guest, you need to re scan the SCSI bus, usually calling rescan-scsi bus command


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USB Passthrough

Assign a USB device to the guest

XML configuration on VM (USB) XML configuration on VM (PCI)


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IPMI tips





Uses an updated IPMI package on the client

IPMI is based on UDP, so, avoid networks that lose packets.


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Thank you!


KVM vs PowerVM


Snapshots - Stoa Social

Best practices in virtualized environments

(PowerKVM)

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(PowerKVM)

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