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August 29, 2008


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Maybe I don't understand the VSS remark, but as far as I know as of 3.5 U2 and VCB 1.5 VSS is supported: http://www.vmware.com/support/vi3/doc/vi3_vcb15_rel_notes.html

I haven't been able to test it though.

Chad sakac

Right - translating what VSS support means has been difficult since it's introduction.

VSS is often used referring to BOTH:

- Volume Shadow Copy services for NTFS filesystem-consistent backup using a freeze/thaw mechanism with Window's system provider, or 3rd party provider

- Volume Shadow Copy services as a 3-way API operation including a writer (think "application integration module"), a requestor (think "backup application running on the host"), and the same provider mechanism used for generic NTFS file-consistent backups.

For example on the latter - Exchange 2003 and 2007 ship with VSS writers (as does SQL server). A VSS requestor calls those VSS writer APIs to initiate application specific behavior during backup and restore. For exmaple in Exchange's case flushing and closing the current open log during backup, handling validation of the backup, and during restore, triggering and handling log replay. In otherwords "application level consistency actions". Then the VSS provider kicks in.

What happens in 3.5 u2 is that now, just like array-based replicas who's vendors created VSS providers that operate inplace of Microsoft's system provider, ESX snapshots now act as a VSS provider, and you get NTFS-consistent backups.

BTW - homework excercise for anyone with XP, or W2K3 or W2K8 - right click on any NTFS volume, go to "properties", then "previous versions" - that's native VSS.

Supporting VSS (and the storport driver stack, which is the big change in u2) is a mandatory pre-requisite to application-integrated VSS.

So, now people who have created VSS requestors for various applications can operate inside the guest, and leverage the native ESX snapshots for the underlying point-in-time copy. Examples of this are most backup applications (EMC's included), EMC Replication Manager and the NetApp SnapManager family (both of which are designed to integrate array-based replicas). EMC Replication Manager supported app-consistent replicas for SQL Server and Oracle in VMs before this change, because there you have other APIs for the same thing (SQL can use VSS and VDI - virtual device interface - not Virtual Desktop Infrastructure, Oracle has hot-backup mode), but this was mandatory for us to support Exchange 2003 and 2007 in VMs with app-integrated backup and recovery.

Does that make sense?

Doug Michalko

RDM's will work with vmotion except if RDMs are used with Microsoft Cluster Services in which case SCSI bus sharing is enabled and the vm cannot be vmotioned.

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