The Glitch - Frequently Asked Questions

FREQUENTLY ASKED QUESTIONS

VMWare vSphere 4

How many virtual machines can I have per physical host server?

vSphere 4.0 & 4.1 support up to 320 virtual machines per host.

How many hosts and virtual machines can be managed from a single VMWare vCenter management server?

vCenter Server 4.1 can manage, up to 1000 hosts and 10,000 powered on virtual machines, and can have up to 15,000 registered VMs.

vCenter Server 4.0 can manage, up to 320 hosts and 3000 powered on virtual machines, and can have up to 5000 registered VMs.

How many hosts and virtual machines can I have in a server cluster or data center?

vsphere 4.1 supports up to 32 hosts and 3000 virtual machines per cluster, and up to 500 hosts and 5000 virtual machines per data center.

vsphere 4.0 supports up to 32 hosts and 1280 virtual machines per cluster, and up to 100 hosts and 2500 virtual machines per data center.

What is 'Linked Mode' in vCenter server?

vCenter's 'Linked Mode' allows you to simultaneously access, search and view the inventories of multiple vCenter server instances. It provides a scalable architecture and visibility of roles, permissions and licenses of all the vCenter Server systems in the linked group.

vCenter Server 4.1, allows you to manage up to 1000 hosts, up to 30,000 powered on virtual machines, and up to 50,000 registered machines, across a maximum of 10 VMware vCenter Server instances from a single console.

(vCenter Server 4.0 can manage 10,000 virtual machines)

What are the hardware and software requirements for a vCenter Server?

A vCenter server must have the following, whether it is being installed as a physical or virtual machine:

HARDWARE
1. A 64Bit Dual-Core processor or two 64-Bit Processors
2. An Intel or AMD Processor running at 2.0GHz or faster
3. 3GB of RAM
4. 3GB Disk Space
5. Gigabit Networking (recommended) - 10/100 minimum

SOFTWARE
1. A supported 64-Bit Operating System:
    Windows XP Professional 64-Bit SP2
    Windows Server 2003 Enterprise 64-Bit SP2
    Windows Server 2008 R2 64-Bit
2. Connection to a Database:
    MS SQL 2005 or 2008
    Oracle 10g or 11g
    IBM DB2 9.5
The Default database installed is MS SQL Server 2005 Express, and is used for product evaluations and demonstrations, it's also sufficient for small deployments of up to 5 hosts and 50 virtual machines.

NOTE: Processor, RAM and especially disk space requirements will increase if both the vCenter server and database are installed on the same machine.

Is vSphere's vCenter a separate product?

This depends on which version of VMWare's vSphere you purchase:

If you purchase VSphere Essentials or Essentials Plus you get a VMWare vCenter Server license as part of your product.

All other versions of vSphere do not, so you must purchase a VMWare vCenter Server license separately at additional cost.

What is HA?

HA stands for High Availability, a highly available system is one that is operational (continuously) for a desirable long length of time.

High Availability (HA) in VMWare terms is used to ensure minimum downtime to all virtual machines in your cluster.

High Availability is achieved by the installation of Agents which monitor each host in the cluster to determine whether they are reachable. Should more than 15 seconds go by without a host communication or successful Ping then that host is declared unavailable and all virtual machines on that host will be failed over (restarted) on alternate hosts with the most available resources.

The HA Agent communications are known as heartbeats which are send every second (by default) over a dedicated heartbeat network.

HA requires shared storage and is only available within a single physical datacenter.

HA is configured, managed and monitored via a vCenter server.


Q.	What is FT?
A.	FT stands for Fault Tolerance, a fault-tolerant system is one that is designed so that if a component fails, a backup system can immediately take its place with no loss of service. Fault Tolerance (FT) in VMWare terms is used to ensure (mission-critical) virtual machines are available at all times (100% availability), this is different to HA where there is a brief period (15 seconds) when virtual machines are unavailable. FT checks individual virtual machines are functioning and creates a (hidden) duplicate of each running VM on a different host so that it can immediately replace any that become unresponsive. vLockstep technology ensures that the duplicate copy (or secondary copy) of the VM stays synchronized with the original or primary VM. FT has a number of specific requirements to perform as expected: 1. Multiple gigabit NICs (minimum two - one for FT logging and the other for vMotion). 2. Hosts to have CPUs from an FT-compatible processor group. 3. Hosts to support HV - Hardware Virtualization in the BIOS. 4. VMs must be running on a supported guest OS. 5. Requires shared storage. 6. VMs must be stored in RDM (Raw Device Map) files or have their VMDK files think-provisioned to enable FT 7. Host certificate checking must be enabled for all hosts. FT is only available within a single physical datacenter.


Q.	What is vMotion?
A.	vMotion migration allows an active (powered-on) virtual machine to be moved from one host to another with zero disruption or downtime, without vMotion VMs need to be manually shut down before they can be moved to another host. vMotion can work in conjunction with DRS (Distributed Resource Scheduler) to load balance VMs across available hosts. During a vMotion migration the entire state of a virtual machine is moved, including current memory content and information pertaining to hardware elements such as NIC MAC addresses, CPU data, Devices and BIOS component configurations. vMotion requirements include: 1. All hosts must if you like able to see all storage used by the VMs 2. Requires at least a Gigabit Network connection to function 3. The same physical networks have to be accessible to all hosts 4. Host CPUs must be compatible with each other (EVC can help) 5. Hosts must have consistent physical & virtual network configurations Up to a maximum of 128 concurrent vMotion migrations can be performed per VMWare vStorage VMFS datastore, with a 1Gbps network able to support 4 concurrent vMotion migrations, and a 10Gbps network up to 8 concurrent vMotion migrations.


Q.	What is a Snapshot?
A.	A Snapshot is a way of preserving the current state (memory, settings and disk) of a virtual machine, it is a point in time copy which can be returned to at any time (it could be thought of as VMWare's version of Window's system restore option). A great way to use Snapshots is during the testing of updates, where a Snapshot is taken of a VM before any changes are made. Should anything go wrong you can use the 'Revert to Current Snapshot' option and get back the machines previous state before the updates were applied. Other options are available in the 'Snapshot Manager' where you have additional options of 'Go To', 'Delete' and 'Delete All': Your current state is indicated by a 'You are here' indicator. Go To : Allows you to move between different snapshots, importantly this option is non-destructive, in that no Snapshots are destroyed. Delete: This option does different things depending upon which snapshot you delete, if you delete the parent of a current snapshot it is consolidated into the snapshot above, if you delete the child of a snapshot it is discarded. Delete All: This option consolidates all snapshots from where ever your 'You are here' indictor is currently, while discarding all others. (this option effectively clears all remaining snapshots).