I have been always hit by customers who have a problem taking an image backup of virtual machines that run a database application. Another repeated question is “when & when not to use Quiescing & VSS with VCB & vRanger”. For that I have decided to write this set of posts hoping to answer these questions. The answer will have the instruction of how to do this as step by step for Vizioncore vRanger, which is a great & easy backup software for VMware, but the explanation apply for any other image level backup software used with VMware, though you will have to adapt the instructions to the backup tool of your choice.
vRanger provides support for Quiescing the virtual machine before it start to backup that VM. The purpose of Quiescing is to ensure that no file system writes are pending when the snapshot is taken, allowing for file system level consistency. Although Quiescing has always been proved to be a great method to backup normal virtual machines, it seems to cause issues for virtual machines which is running a database. Example of virtual machines with database & where it’s recommended to disable Quiescing is MS SQL Server, MS Exchange, Active Directory, and so on.
For VMs which run a database, it’s highly recommended to stop Quiescing. Though not Quiescing a virtual machine before backing it up you will end up with a crash-consistent image (Restoring a crash-consistent image is essentially the equivalent of rebooting a server after a hard shutdown.). Although most applications & operating systems today can sustain a sudden shutdown, most enterprises will not accept to take that risk for critical servers. As database servers are mostly critical servers, then a crash-consistent images might not be the desired solution. For that case, vRanger offer VSS (Volume Shadow Copy Services) which can get you a transactionally consistent backup image. For you to benefit from this feature, the application you are backing up has to support Microsoft VSS. Example of applications which support VSS are MS SQL Server, MS Exchange, & Active Directory.
The message of this document:
1- Virtual Machines which does not run any database, you are recommended to enable Quiescing. As running Quiescing before the backup will give you a file system level consistent image, which is a lot better than a crash-consistent image.
2- Virtual Machines running a database tend to face issues when Quiescing happen, so it’s recommended to disable Quiescing on database servers. If the database application being used support Microsoft VSS (Active Directory, MS SQL Server, MS Exchange, & So on) , then its recommended to enable VSS which will provide you with a transactionally consistent backup image.
From above you will figure out that the way you handle your vRanger backup setting is depend on the server being backed up is a database server, or a non database server. For that, the instruction is introduced as how to handle it for non database server, then how to handle it for database server and titled as below:
Vizioncore vRanger (Previously ESXRanger) Quiescing & VSS Setting for non-database Virtual Machines
Vizioncore vRanger (Previously ESXRanger) Quiescing & VSS Setting for database Virtual Machines