VMware FT

With the announcement of the VMware blogging contest I thought I would add my two cents, my reasons for doing this are one it gives me an opportunity to blog about something different to my usual support, installation and administration posts and second of all it has meant I can focus on some of the new VMware vSphere features in depth one at a time.

There are already numerous white papers and technical documents surrounding VMware FT so I didn’t want this just to become a rewrite of one of these, I thought I would share some use cases that I have experienced over my past few months installing vSphere, some findings to help you getting started and a step by step overview of enabling FT on your VM’s.  The work I undertake is mainly in the SMB environment so this will maybe give those that work mainly with Enterprise environments another view and also will hopefully be useful to those at all levels of are considering or wanting to know more about VMware FT.

Technical Papers

First the technical papers I spoke about earlier

• http://www.vmware.com/resources/techresources/1094
• http://www.vmware.com/resources/techresources/10058
• http://www.vmware.com/resources/techresources/10040

What is VMware FT?

VMware FT provides continuous protection for the protected VM’s during a host failure, it does this by creating a live shadow of the protected VM and keeps the primary and secondary VM’s in sync using lockstep technology, this means commands that are completed on the primary VM are mirrored in the same order on the secondary VM. If a host failure then causes the VM to fail the secondary will take over with no disruption, FT will then automatically create a new secondary VM to continuously protect your VM once again.

What VMware FT isn’t

VMware FT won’t provide you any protection for storage failure, only host failure.

What do I need to protect my VM’s with FT?

• vSphere Advanced or above
• A minimum of 2 hosts but 3 to allow for continued protection in the event of 1 host failure
• Your hosts should be on the FT compatibility list
  • http://www.vmware.com/resources/compatibility/search.php
  • Please be aware that this list seems to be a work in progress at the moment and many FT compatible systems aren’t listed like those from HP. Please check with the server manufacturer or server specialist for more information.
• Your CPU’s and Guest OS should be on the FT compatibility list
  • http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1008027
• There are also a large number of pre-requisites for your VM’s that you must understand and meet before enabling FT on your Guest
  • This is the best article on FT pre-requisites that I have found >> http://www.ntpro.nl/blog/archives/1090-Fault-Tolerance-Checklist.html
  • For me among the main points are
    • Only 1 vCPU for guest VM’s
    • Snapshots are not supported on FT proteced VM’s
    • No RDM’s
    • VM Disks must be thick eager zero’d
• Two dedicated 1Gb links for FT logging

Use Cases

With all the pre-requisites and limitations of VMware FT a lot of people in the communities are saying they can see that this is the start of must have feature but until it supports multiple vCPU’s it will have little use. Whilst this maybe the situation for enterprise customers, a lot of SMB customers are able to start making use of this feature now. Many smaller companies have small IT teams but have servers that run mission critical functions that sometimes will have considerable consequences with any unplanned downtime.

Legal Firm

I have recently completed a project for a legal firm, their Exchange server was at the heart of their business and any downtime during the limited amount of time their barristers have to access email could be extremely costly. Although VMware HA would cover their risk of server failure, they couldn’t afford to trust an unclean power down and the amount of calls to deal with whilst the servers were booted on another host would be huge. With only 2 IT staff managing their IT infrastructure learning, monitoring and maintaining a complicated replication or clustering technology would not be possible. So after viewing a demo of VMware FT it was clear this was a must have feature for them. After initial analysis and ensuring their Exchange server could work within the limitations of FT their Exchange server was virtualised and is now protected with VMware FT.

Hedge Fund

Similarly to the Legal Firm I am currently investigating the possibility to use FT to protect a number of servers within a hedge fund, again with a small IT team and mission critical servers with disastrous consequences if the server was to go down during the working day. 

How easy is it to protect a VM with FT?

Once you have configured your host for FT with the needed VMKernel port for FT and check the various pre-requisites you just need to complete the following step to protect your VM.

Step 1

Right click on your VM and choose the “Turn On Fault Tolerance” option under Fault Tolerance

You will get a warning regarding the disks for your VM needing to be eager zeroed, that automated DRS will be disabled and that the memory reservation for your VM will be changed to equal the memory size of your VM.

FT will create the secondary VM

vMotion is then used to copy the state of the VM to the secondary and enable FT

Once FT is enabled you will see the colour of the FT enabled VM has now changed to a deeper blue.

If you look on the summary tab of the protected VM you will now see the FT information

and if you look on the ESX host where the secondary is located you will see the secondary VM

Once enabled you are also able to test failover and test restart secondary, which will simulate the failure and recreation of the secondary VM.