vSphere replication 6 and Linux guest OS quiescing

[kwg66]

I have scoured everywhere for more details on this.. and find NOTHING anywhere..  oh wait, I found this statement in a VMware KB2041909 that was updated Dec 28, 2016:

"vSphere Replication does not support quiescing for Linux" 

Can someone from VMware, or other knowledgeable vExpert, shed light on this...  

When reading the release notes of vSphere Replication 6, it actually states the following:

"Linux guest OS quiescing: introducing Linux guest OS quiescing service to provide file-system level crash consistency to replicated Linux-based VMs."

Is it just me, or does the "crash consistency" part of this statement stand out like a soar thumb?    I was under the impression that when a snapshot is taken without proper quiescing of the OS it will create a crash consistent image, and when properly quiesced the image becomes transaction consistent..

I did read long time ago that in the VMtools directory you can place files in it that contain your custom scripts to freeze and thaw, is this what this is referring to?  but if yes, this isn't new at all, I read this many years ago.. and even now can't find any reference to documentation on it. 

Forget the points, beer for anyone who can share some expertise on this one..  but only when you are in Boston, I can't afford to travel to buy you a beer..   

[mvalkanov · Accepted solution]

Hi,

VR 6.0 and next support file-system level quiescing for Linux guests.

See "Linux guest OS quiescing: introducing Linux guest OS quiescing service to provide file-system level crash consistency to replicated Linux-based VMs." at VR 6.0 release notes - VMware vSphere Replication 6.0 Release Notes

See also "Linux Quiescing Support" section at Interoperability Pages for vSphere Replication 6.5 after selecting category "Guest OS Quiescing Support" at the dropdown.

AFAIK the mechanism is freeze and thaw. It has been supported for backup tools (VDP and similar) and with VR with version 6.0 and next. Earlier VR versions (before 6.0) did not have such integration.

I have filed feedback on KB 2041909 to be updated.

Regards,

Martin

[kwg66]

@Martin - Thanks for filing the feedback on the KB. 

Can you point to any documentation on how this is set up and configured?

Thanks

[vbrowncoat]

There is nothing to setup or configure as far as I know. If your linux version is supported (vmtools will confirm it) you will be able to turn it on in the replication configuration

[kwg66]

@gs_khalsa - Thanks for this tidbit. 

This brings up the question about what VMware tools will be supported for this quiescing operation.  Open source or native VMtools available on the host, or both? 

[sguk]

Is there any further development on quiescing linux in general?

Details are very sketchy and have been for years. We've just discovered our replicas have file errors, probably repairable by fsck but none the less, they have them.

2 VM's have quiescing on in Nakivo

2 have it off as one Centos 6 which has a known bug for crashing under quiesce

However, one of those with quiescing on is a VM with the errors. I then discovered the config setting

disk.enableuuid

True=Application-Consistent, False=Crash-Consistent.

It was not set on 2 VM's and was set to false on the others, which apparently makes them crash consistent. However, in the logs quiescing is mentioned.

Reading elsewhere online it says that no quiescing is done on Linux, only if pre freeze/post thaw scripts are used. Right.... so what is VMtools doing in the logs?!

And where do VMWare actually clarify this?

Reading many more threads for hours (already did this 18 months ago) and I can't actually find any "trusted" scripts which seem to be verified. All very odd.

For years now this has been a grey area, I just wish it was cleared up once and for all. It would be good to know how VMWare addressed it in their own replication.