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rickardnobel
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FT: Any risk for application breakdown when failover?

When using a VM that is protected by the Fault Tolerance feature - what will happen if the first host fails at some extremly critical point of time and the secondary VM is just some milisecond after? I am thinking of some kind of database server or similar, what if something is sent over the network from a client and that action gets commited back to the client, and the microsecond later the host fails. When the secondary takes over - is there any risk for application error or corruption from this?

My VMware blog: www.rickardnobel.se
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vmroyale
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Hello.

Paraphrasing this or reducing it down to a simple answer won't do it justice.  The answer lies in here.

Good Luck!

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com

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vmroyale
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Hello.

Paraphrasing this or reducing it down to a simple answer won't do it justice.  The answer lies in here.

Good Luck!

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
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rickardnobel
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Thanks for the link. I have read it now and I do think I found the answer to my question. I think most of it can be found in the following text:

"the primary VM may not send an output to the external world,
until the backup VM has received and acknowledged the log entry associated
with the operation producing the output"
My VMware blog: www.rickardnobel.se
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idle-jam
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we have use it a lot and it works very very well even for those monitoring, batch transactional type of application. i would advise you testing it yourself as no one can really speak on behalf of your applications and needs.

rickardnobel
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idle-jam wrote:

we have use it a lot and it works very very well even for those monitoring, batch transactional type of application. i would advise you testing it yourself as no one can really speak on behalf of your applications and needs.

Thanks for the input. I am not thinking of any perticular application or service myself, just want to understand the general funcationality of FT.

Have you had any "real" failovers? :smileygrin:  After reading the document (above) I realized that the techology is quite more advanced and the general problems that has to be taken care of is more than I thought. Impressive!

My VMware blog: www.rickardnobel.se
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bulletprooffool
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In short - No.

All writes are fully processed / committed at both ends - yet the CPUs run independently.

In other words, an application crash / bluescreen will kill both VMs, but the FT will not affect your application.

One day I will virtualise myself . . .
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