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JamesSarasota
Contributor
Contributor

How VMWare FT handle SQL 2012 transaction?

Hi All,

     Consultant recommends VMWare FT for SQL server 2012, we used to have SQL server cluster on Physical machine.

So now my organization go for VMWare FT with SQL server without any HA in SQL Server or any HA for VMWare.

I do not understand how VMWare FT handle transaction for SQL Server.

In the past we all know that SQL can not do hot backup of database file that why FT make me confuse.

Due to limitation of Consultant time so we can not ask him to set up test environment for us, so I can not do any invasive test.

I do agree to move SQL database to VMWare but using VMWare FT to replace SQL Clustering, I need to search for more detail.

If any guru can explain the mechanism how FT handle SQL transaction or provide idea about this scenario, I will be really appreciated.

Thank you in advance.

JJ

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MKguy
Virtuoso
Virtuoso

FT is not an application specific mechanism so it doesn't "handle SQL transactions" in the way you put it.

Think of FT as a kind of constant replication/vMotion: You have a VM running on one physical host and this VM has all its CPU instructions, memory access etc. mirrored over the network to a secondary shadow VM on another host. If the primary physical host fails, the shadow VM is activated and things keep running as if nothing happened.

FT doesn't care about what kind of application you're running inside the VM, it's completely application-agnostic since it operates by mirroring at the CPU/memory layer.

It's important to understand that FT protects against physical host failures and not against any OS/application side issues.

Server rebooting for monthly patchday or whatever reason? SQL Server process crashing? OS bluescreening? Disk running out of space?

It's a cool feature, but in the end FT won't protect against any of these, and in my experience physical hardware failures with decent server and DC hardware are much less common than software failures or human error.

This is why I would not recommend FT for MS SQL Server when you can have application-level HA through SQL always-on clustering, which is a much better solution.

Also FT has many restrictions and caveats, like maximum 4vCPU (since vSphere 6 only), no snapshots and more. You need low-latency and high bandwidth for the FT traffic at least 10Gbit/s to get acceptable performance.

Besides for physical failures you have normal vSphere HA already. Yes, you will see a short outage when VMs are restarted on another host, but you should ask yourself are the added complexity and restrictions of FT worth the trouble?


Read this whitepaper for a detailed overview on how FT works:

http://www.vmware.com/files/pdf/techpaper/VMware-vSphere6-FT-arch-perf.pdf

VMware Fault Tolerance FAQ (1013428) | VMware KB

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