Administrator's Guide

Overview 21
can use the FRS GUI to restore the production volumes from the most
recent data copy or another point-in-time copy on the recovery volumes.
Volume Shadow Copy Service (VSS)
Microsoft’s VSS manages creation and maintenance of shadow copies of
production data for backup and recovery. This service works under the
control of the FRS interface and the Windows OS file system services.
When requested by FRS, VSS coordinates with the writer and hardware
providers to perform shadow copying of production data to the recovery
volumes. The shadow copies contain static copies of all files, such as
databases, transaction logs, and checkpoint files.
Copy terminology
Understanding how Microsoft VSS terminology corresponds to standard IT
industry terms for data copying makes it easier to understand what VSS
does. The following paragraphs explain the terminology.
Microsoft generally refers to a VSS copy as a “volume shadow copy.”
When created using HP FRS and HWP, this type of copy is a static replica
of an original volume’s contents. It is keyed with a GUID to allow
identification of the parts of a shadow copy set that span multiple volumes.
Microsoft also refers to a VSS copy as a “plex,” commonly known in the IT
industry as a “split mirror.”
When you use an EVA array to make the shadow copy, the array makes
what is known as a “snapclone.” An EVA Snapclone is a complete clone
copy of a specified Virtual Disk (LUN). EVA snapclones are available
almost immediately. This is accomplished by creating a point-in-time copy
and making it immediately available by pointing to data on the original
volume while continuing to copy data to a secondary volume in the
background. When copying is complete, the snapclone is a static
point-in-time copy of the original.
The shadow copies made on the EVA array using VSS, FRS, and HWP are
always static, point-in-time copies.