Posted by: Beth Pariseau
data backup, Storage and server virtualization
Among the updates Symantec announced today to its NetBackup 7.0 and Backup Exec 2010 backup applications are enhancements to the granular backup of applications running in virtual servers, in part through integration with VMware’s new vStorage APIs for data protection.
These APIs are among the more widely hailed updates in vSphere 4 for storage pros. They promise to eliminate the cumbersome VMware Consolidated Backup (VCB) from the infrastructure and allow existing enterprise backup software tools to make backups directly from virtual machines, the same way they’ve been doing for physical servers.
Backup Expert W. Curtis Preston has been among those claiming the vStorage APIs for data protection will be a boon for improving virtual server backups, but points out in light of Symantec’s announcement that its approach of integrating NetBackup 7 with VMware’s VSS implementation leaves something to be desired.
According to Preston’s research, VMware’s VSS support will perform consistent backups of a data volume, which he calls “table stakes” in the snapshot backup market. But Preston says the VMware VSS integration can’t perform application consistent backups with Windows 2008 hosts, and in the case of either Windows 2003 or Windows 2008 hosts, it won’t notify the application when a recent backup has been made or refresh where it starts tracking incrementally changed data. (Think of it as resetting the trip speedometer in a car after a trip is finished).
“What this means is that anyone wishing to get proper backups of applications in Windows must run an agent of some kind in their guests in order to make this happen,” Preston wrote in a Jan. 11 blog post. He goes on to warn, “This means that any backup tools that are using only VMware’s infrastructure are going to have the same limitations.”
Symantec declined comment on the limitations cited by Preston. VMware officials confirmed that for Windows 2008, vSphere supports backups at the operating system level (as opposed to the application or transactional level). They also confirmed that vSphere’s integration with VSS doesn’t make the application aware it’s backed up (see the trip speedometer analogy above), but said through a spokesperson, “Back in the old file-level days there used to be an archive bit that was changed, and hence the application was aware of the backup. [But] the question is, does it really matter for the image level backup?”
“This has nothing to do with the archive bit,” Preston responded in an interview with Storage Soup. “Applications need to know when to truncate their transaction logs.” If transaction logs aren’t truncated, in the case of a database application, “they’ll eventually fill up and crash the database.”
VMware plans to continue innovating around VSS backups, the spokesperson added. Preston’s blog post also mentions VMware is working on more granular VSS support.
In the meantime, I’m wondering if anyone out there reading this in blogland has personally encountered these problems, or better yet, any workarounds they would like to share.