Simple KVM service documentation

Guests : Information on managing KVM guests
Hosts : Information on managing KVM hosts

KVM Server reboots

KVM host reboots will be announced a week in advance, and these reboots will only be cancelled for very good reason. Reboots won't go ahead until the details have been signed off by each affected unit on the KVM server scheduled downtime page. The reboots will take place early morning (8am). Only very critical services will be migrated to another server - if possible. Other guests will be suspended or rebooted depending on what KVM allows.

The MP unit will try and minimize the number of KVM host reboots - we expect 2-3 reboots per host per year.

(Agreed at the 25/09/13 operational meeting)

There's a page which details scheduled downtime for the KVM servers.

Which server for a new KVM guest?

For a Forum-based VM which doesn't have to be very speedy, choose girassol. Its CPU cores are slightly slower than those on the other KVM servers but it has many more of them, so your VM is likely to get a core when it needs one. If it does need a faster CPU, choose the less loaded of the other two Forum-based KVM servers.

For an AT-based VM choose banjo or mandolin, they're identical.

For a KB-based VM choose amarela or vermelha, they're identical.

There is a simple web report summarising the current usage of the KVM servers.

Host click host for details	Memory (GB)	Storage Locations see below	Site	Hot Migration see below	Comments
girassol	256	local disk (gp3, gp1)	Forum	Yes, between girassol, gaivota and azul.	SL7. Fully supported. Has many more CPU cores than the other servers, but they're a little slower. Put your less demanding VMs here.
gaivota	256	local disk (vp3, vp1)	Forum		SL7. Fully supported.
azul	128	local disk (ap1)	Forum		SL7. Fully supported.
banjo	192	local disk (bp1)	Appleton Tower	Yes, between banjo, mandolin and oyster.	SL7. Fully supported.
mandolin	192	local disk (wp1)	Appleton Tower		SL7. Fully supported.
oyster	128	local disk (op1)	Appleton Tower		SL7. Use at your own risk. Oyster is our test KVM server and may be rebooted at very short notice
amarela	128	local disk (ap1)	JCMB	Yes, between amarela, clavichord and harpsichord.	SL7. Fully supported.
clavichord	256	local disk (cp1)	JCMB		SL7. Fully supported.
harpsichord	256	local disk (hp1)	JCMB		SL7. Fully supported.

About Storage Locations

A guest's disk space is created in one of the host's storage pools. A pool can be a local directory, an NFS mounted directory or an LVM volume group. We are using LVM volume groups for our KVM hosts.

To see how much space is available in a pool, login to the host server, nsu then /sbin/pvs. The "VG" column in the output is a shortened form of the pool's name, so it should be obvious which pool is which.

About Migration

Hot migration is where a virtual machine is moved to another host while it's still up and running. The virtual machine and its users are unaware of the move; it just keeps on running. There is no downtime. Hot migration works between KVM hosts which are at the same site - because they need to be carrying the right subnet. Please ask the MPU to do the migration for you, don't try it yourself.

Bridges

A KVM host has one bridge interface per subnet that it supports. The default bridge, named br0, will be connected to the same subnet as the KVM host. Other bridges are named eg br33 for wire-s33. Note that the KVM hosts are not, themselves, multi-homed: this makes it much easier to add and remove subnets for the KVM guests.

Further KVM documentation

• Red Hat Enterprise Linux 6 documentation list including
  • Virtualization Administration guide
  • Virtualization Getting Started Guide
  • Virtualization Host Configuration and Guest Installation Guide
  • Virtualization Security Guide
• virt-manager home page

-- AlastairScobie - 28 Oct 2011