More and more information regarding the requirements of VMware Fault Tolerance (FT) feature are becomming available. Here's a few very useful posts that I've found regarding these requirements.
http://www.techhead.co.uk/can-you-run-vmware-vsphere-fault-tolerance-ft-on-an-hp-proliant-ml110-or-ml115
http://www.ntpro.nl/blog/archives/1061-CPU-compatibility-with-VMware-Fault-Tolerance.html
** Update 8-10-10 **
Here's an awesome link that outlines some very detailed requirements and limitations of Fault Tolerance (FT):
http://communities.vmware.com/blogs/vmroyale/2009/05/18/vmware-fault-tolerance-requirements-and-limitations
Here's a nice and short overview of Fault Tolerance (thanks to TechHead.co.uk):
Key Features of Fault Tolerance
The following are some key features of VMware Fault Tolerance as provided in VMware’s FT white paper:
• Runs on standard x86 based servers, vendor neutral.
• Supports standard unmodified guest operating systems and
applications.
• Protects dozens of guest operating systems already supported
by ESX, including 32- and 64-bit Windows, Linux, Solaris, and many other legacy guests.
• x86 hypervisor-based solution; integration with virtual machine technology, operating system neutral.
• Support for all emerging applications frameworks that have
not yet evolved their own clustering solutions.
• Support for existing virtual machines.
• Single image management: virtual machine is installed and
managed in the usual way as a single image; no need for
additional operating system and software licenses.
• vLockstep guarantees: the primary and secondary execute
exactly the same x86 instruction sequences.
• Transparent failover with no data or state loss in the virtual
machine; all state, including storage, memory, and networking
is preserved even in the face of catastrophic hardware failures.
• Potential different physical locations for primary and secondary
to guard against campuswide or buildingwide failures.
• Automatic re-establishment of fault tolerance after hardware
failures.
• Integration with HA and DRS that are responsible for selecting
a new secondary host after a failure; no manual steps during
failover or after recovery.
• Failing systems can be returned to the HA cluster after repairs
without any additional FT reconfiguration.
• Component failover when combined with network teaming
and storage multipathing.
• No additional installation; FT is a built-in feature of VMware
ESX.
• Mixing FT and non-FT virtual
Current Fault Tolerance Limitations
There are however a couple of limitations:
Compatibility – VMware Fault Tolerance will only run with the following models of CPU and above:
VMware Fault Tolerance requires Intel 31xx, 33xx, 52xx, 54xx, 55xx, 74xx or AMD 13xx,23xx, 83xx series of processors or above.
Update (7-16-09): A nice VMware KB article for CPU compatibility is located here:
http://kb.vmware.com/kb/1008027
See also the NTPro.nl link at the top of this post for an even more detailed CPU list. Also see the VMware website at
http://www.vmware.com/products/fault-tolerance/ (near the bottom of the page) for details as well.
The reason for this being that these models of CPU have additional physical processor extensions required by the vLockstep technology.
It’s in the family – When using FT in a cluster all physical ESX hosts must be running CPU’s from the same family. For more information on this see Eric Sloof’s informative posting here which has an easy to follow table.
vCPU – FT, at this stage, will only with work VM’s with a single vCPU – at this stage though expect to see multi-vCPU compatibility in the future.
Thin Provisioning – FT is unable to protect VMs that are running thin provisioned disks.
