What is the difference between the snapshots?

[Corochun]

Hi All,

Maybe you can advise: if snapshots are not recommended in production, what is the differense between mannually taken snapshots and those ones taken by VCB? The statement from VCB administration guide "Consolidated Backup flushes the transient writes in the guest operating system and suspends any further writes for a few seconds in order to create a crash-consistent virtual machine image" tells me nothing. How does VCB ensure consistent backup? Is the same technology in use when i create snapshot manually? Can backup consistency be guaranteed without VMware tools installed on the VM i want to backup with VCB?

Thanks,

Kirill.

[Corochun]

Related question: LGTO SYNC driver is installed with VMware tools. I haven't found any useful information on this yet, but think this driver is in charge of data consistency. What is LGTO SYNC for?

[Michelle_Laveri]

I imagine its the VMware Sync Driver - which is used as part of VCB as a part of a "quiescing" process prior to back. You know flush file system cache, start back up now...

It's generally regarded that the support that VMware added in later version of VMware Tools for Microsoft VSS is superior...

Regards

Mike Laverick

RTFM Education

http://www.rtfm-ed.co.uk

Author of the SRM Book: http://www.lulu.com/content/4343147

[Michelle_Laveri]

Hi All,

Maybe you can advise: if snapshots are not recommended in production, what is the differense between mannually taken snapshots and those ones taken by VCB? The statement from VCB administration guide "Consolidated Backup flushes the transient writes in the guest operating system and suspends any further writes for a few seconds in order to create a crash-consistent virtual machine image" tells me nothing. How does VCB ensure consistent backup? Is the same technology in use when i create snapshot manually? Can backup consistency be guaranteed without VMware tools installed on the VM i want to backup with VCB?

Thanks,

Kirill.

OK. A production use of VMware Snapshots is hot-backup of the virtual machine by VCB, esxPress, vRanger, Veeam Backup. Any hotbackup of the VM MUST use snapshots.

The snapshots you manually make are no different. The only difference is when you backup vendor utilizes them - they are ALWAYS temporary, just for the period of the backup window. However, many vendors backup code varies in quality on how much they log/check that the remove of the snapshot has been successful. Orphaned snapshots are not unheard of, and if left unchecked will grow incrementally. For this reason many people run scripts daily/weekly checking for snapshots over a certain size...

To have a consistent backup you need some kind of sync driver - either microsofts or VMwares. Running a VM with VMware Tools is strongly recommended unless you happy to live with reduced performance. Almost EVERY virtualization vendor has some kind of package that is installed to the guest OS post the OS installation.

Not sure why the VMware statement "tells me nothing". It makes perfect sense to me. I guess the argument is good is this quiescing process. Generally, the MS VSS driver support that new versions of VMware Tools ship with, is regarded as being more "application aware" than VMware's Sync driver. Early reports indicated that the VMware Synch driver struggled with transactional based systems like AD, SQL and Exchange...

Regards

Mike Laverick

RTFM Education

http://www.rtfm-ed.co.uk

Author of the SRM Book: http://www.lulu.com/content/4343147

[Corochun]

What I meant is that I don't understand the technology behind the statement and its limitations. If the mechanism is the same as used for manual snapshotting, than VCB has the same limitations. If transactional system (Oracle for example) suffers when snapshot is taken, than it can't be backed up with VCB.

Thanks,

Kirill.

[Michelle_Laveri]

Well, this is how interpret it...

There is two types of snap synch driver. One that results in a consistent backup (MS VSS), and one that results in crash-consistent backup (MS VSS). As we know a crash-consistent backup, is akin to us hard powering off a machine, and then copying the files of the disk. Any transactions held resident in memory would be lost, although I think VMW by flushing caches is trying to make the backup as near complete as they can. It's this state that VCB and other backup system use as their defaults. Since then VMware has integrated its VMware Tools to allow for called to MS VSS copy. It's my understanding that this method is more reliable from a SW perspective than the VMware Sync driver. Affectively, I think VMW have thrown in the towel with their own driver, and accept the MS one because it results in a more consistent backup. The integration with MS VSS from VMware Tools should mean consistent backup is taken... I guess VMware are retaining their own Synch driver for GOS that don't support MS VSS, or have no eqivilant...

Who is your backup vendor? I think you need to take this question to them - and see what they say/recommend...

>Regards

Mike Laverick

RTFM Education

http://www.rtfm-ed.co.uk

Author of the SRM Book: http://www.lulu.com/content/4343147

[Corochun]

Thanks, i see it more clear now.

In my opinion it also depends on service you are running in a VM. For example Oracle has it own way to ensure consistency, and it conlicts with LGTO driver. I think the same issues might be with other services.

If you can advise what to read on the matter, it would help a lot.

Thanks,

Kirill.

[Michelle_Laveri · Accepted solution]

K. If the VMware Sync driver conflicts with your Oracle build you should be able to do a custom install of VMware Tools for those builds, and deselect the driver...

As for reading on this. Most books (including my own) don't really go into this level of detail.

I did a google wack and this is what I found:

http://communities.vmware.com/thread/217833

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=596216...

http://technet.microsoft.com/en-us/library/cc785914(WS.10).aspx

http://invurted.com/vss-vs-vcb/

There appears to be cases where people have HAD to remove VMware Sync driver because it has caused an issue....

Regards

Mike Laverick

RTFM Education

http://www.rtfm-ed.co.uk

Author of the SRM Book: http://www.lulu.com/content/4343147

[Corochun]

I consider this as an answer, thanks.