What exactly is "precopyStunTime"?

[FL0G]

When I vMotion a virtual machine, I can see the following entries in the hostd.log on the destination ESXi host.

2015-10-26T14:58:22.441Z [301D7B90 verbose 'Vcsvc.VMotionSrc (1445871396819489)'] Set source task result vm downtime to 115329

2015-10-26T14:58:22.441Z [301D7B90 verbose 'Vcsvc.VMotionSrc (1445871396819489)'] Set source task result precopyBandwidth to 576226700

2015-10-26T14:58:22.441Z [301D7B90 verbose 'Vcsvc.VMotionSrc (1445871396819489)'] Set source task result precopyStunTime to 8491272

What exactly is precopyStunTime?

I assume that "vm downtime" is the switchover time at the end of vMotion. The precopy phase where the memory is copied in the first iteration does not require a Stun, so it does not make any sense? I don't think that this has anything to do with "Stun During Page Send" beacuse I also see this with SDPS Disabled (Migrate.SdpsEnabled=0).

When the precopyStunTime is in "us" (like vm downtime) this would result in 8 seconds in the example above. This would be a pretty long stun?

The question is not specific to a ESXi version, but the version I am running here is VMware ESXi 5.1.0 build-2323236

[homerzzz]

As far as I know, that is when the VM is "paused" or quiesced on the source, final pages are transferred and the started on the destination.

Yes, 8 seconds is a long time. What kind of transfer rate are you getting?

[FL0G]

You are refering to the "Switchover" at the end of vMotion where the VM is stunned to copy the last dirtied pages. But what is "vm downtime" then? I also can't "feel" the 8 second stun. It's stunned, but not for longer than a second.

Another strange fact is that the precopyStunTime is always close to the same regardless of whether the VM is under load or not. I've also written random data to the memory. No changes...

The first precopy iteration takes about 100 seconds.

You can see the transfer rate in the logfile too: 576226700 = 4,6 Gbit/s or 580 MByte/s.

Still no clue what precopyStunTime is...

[vbondzio]

It is the time spend tracing the pages at the beginning of the vMotion. At least since 6.0 you wouldn't notice a "stun" though, more of a slowdown if at all.