VSS vs VCB
The problem: Getting consistent backups of Windows, SQL, Exchange and Oracle while hot backing up VM’s at the VMDK level
In the physical world you have backups that use Volume Shadow copy to backup files and databases. All the tape backup vendors use this when working with SQL, Exchange and now the latest version of Oracle support VSS also. This allows for consistent backup of SQL, Exchange and Oracle.
What has VMware done to try and help:
When Vi3 was released VMware brought quiesce option to snap shots. What does this mean? What this does, is you have the option to quiesce the file system before you open a VMware snap shot. If installed, the SYNC driver holds incoming I/O and flushes all dirty data to a disk, thus making file systems consistent.
This can be called when adding snap shots to allow for a better backup.
Make sure to see the Key words here file “file systems consistent”
See this link
http://www.vmware.com/pdf/vi3_vm_backup.pdf
Page 40
Issue with VMware’s SYNC Driver
1. Not Application/Database Aware
2. Does nothing with transactions in memory
3. We Found in Dec 06 that this SYNC driver has caused issue with VM’s that contain Active Directory, SQL, and Exchange. We had customers calling in with production data running in the VM not the backup. That is when we added to the option to not use quiesce option to avoid this issue. VMware has confirmed this is a known issue.
Here is a VMware tech note on the issue…
http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&externalId=5962168
Any one that tells you the VMware quiesce is ok and takes care of everything is not correct we have seen first hand and VMware has confirmed there is an issue with it.
SOURCE: http://supportforums.vizioncore.com/forums/thread/7241.aspx
Posted on May 23rd, 2008 | By: Adam | Filed under VMWare
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