Would you use VMware Tools Quiescence on a busy server?

[mschlott]

Using application aware processing is breaking the SQL backup chain and causing my DBAs scheduled differential backups to fail. It looks like the only workaround is to disable application processing in Veeam. Since I need to get recoverable backups, I think I need to enable VMWare Tools Quiescense in my backups.

If I enable VMWare Tools Quiescense on a highly transactional database server, am I asking for trouble, or should this be safe? If this is not a good idea, then I need to find a different way to backup my SQL servers.

mike

[tsightler]

Do you have log truncation disabled? This should prevent a VSS backup from breaking a traditional full/differential backup chain.

[mschlott]

I have "Do not truncate logs" checked under Transaction logs.

This is what my DBA is running.

BACKUP DATABASE MYDB
TO DISK = '\\MYSERVER\SQL\SQL2008DEV\BACKUP_FULL\MYDB_v2.bak'
WITH DIFFERENTIAL
GO


And here is the error he is getting.

Msg 3035, Level 16, State 1, Line 1
Cannot perform a differential backup for database "MYDB", because a current database backup does not exist. Perform a full database backup by reissuing BACKUP DATABASE, omitting the WITH DIFFERENTIAL option.
Msg 3013, Level 16, State 1, Line 1
BACKUP DATABASE is terminating abnormally


My guess is that the diferential is based on my Veeam backup and not his full backup, which ran on saturday. I verfied that he can run a full backup, then an differential. If I run a Veeam backup with VSS enabled, he can no longer run a differential.

[tsightler]

I agree that it appears this is what is happening. I would suggest opening a support case as, in my opinion, the primary use case of the "do not truncate logs" is so that it does not interfere with other backups. If you are running recent vSphere (4.1 or greater) with latest VMware tools, you should be able to get application consistency with VMware tools quiescence. This article explains the versions, features and requirements to do this fairly well:

http://www.vmguru.com/articles/data-pro ... -explained

[tsightler]

It does appear that is updating the differential base DSN even with log truncation disabled as this appears to be the default when VSS is called. I'm not sure if there is a way to avoid this even if you use VMware tools quiescence since it will be calling the same VSS providers to get application consistency. I'm thinking perhaps it will work since I believe it calls them as COPY ONLY only but it would need to be tested.

[mschlott]

I have not tested using only VMWare Tools Quiescense yet. My concern is that even if this works, that it is a bad idea. The below is from the documentation, which would indicate I should not use VMWare Tools Quiescense on a busy server. This leaves me with no options to back up my OS other than traditional backup. I don't think opening a support case will help because Veeam is working as designed. I think this is just a documented limitation. If I'm wrong, let me know. I love using Veeam for backups. It just may not be a fit for my SQL servers.

VMware Tools Quiescence
Veeam Backup & Replication provides support for VMware tools quiescence. When taking snapshots of a running VM, VMware tools quiesce a file system to ensure integrity of on-disk data. To that end, VMware tools use the SYNC driver that holds incoming I/O and flushes all dirty data to a disk, thus making the file systems consistent.
However, when you back up highly transactional applications such as Active Directory, SQL, Exchange Server, use of VMware tools quiescence may cause issues. Under heavy I/O load, the delay in I/O may become too long. If writes issued by these applications get delayed for too long, the applications may stop responding.
For this reason, the Enable VMware tools quiescence option is disabled by default. It is strongly recommended to leave this option disabled if you are backing up or replicating Windows systems that support Windows VSS — for these systems, it is recommended to use the Enable application-aware image processing option.

[tsightler]

I think the documentation is slightly out of date and based on versions of VMware tools that did not include VSS processing. VMware tools no longer even includes the "SYNC" driver and recommends removing it for old systems that have old versions. This driver was indeed a disaster for highly transactions systems.

http://kb.vmware.com/selfservice/micros ... Id=1009886

As shown in the link from my previous post, VMware tools has supported VSS application consistency since vSphere 4.1. It is not as robust or have the application specific knowledge as Veeam's custom AAP feature, but it does place the applications into a consistent state for the snapshot. This is regularly used by customers that, for one reason or another, cannot leverage Veeam AAP.

[mschlott]

Thanks for the feed back. I'm going to do some testing and see what happens.