HP Application Recovery Manager software A.06.10 Concepts guide (March 2008)

Because there is a separate physical copy of data, there is a higher likelihood
that these target volumes will remain intact and available, if the array hardware
experiences a partial failure that impacts the source volumes.
Snapshot replication
Snapshot replicas are created at a particular instant and are immediately available
for use. Unlike split mirror replicas, no data is copied initially, but rather, a duplicate
of the original storage is created through virtualization. At that moment, the replica
is a virtual copy. The actual data is shared by both source and replica.
After that, when data in the source volumes is changed, the original data is first
copied to the snapshot and then the source data is updated. Over time, the snapshot
references partly its own independent data and partly shared data (in the form of
pointers to unchanged source data). However, from the host or operating system’s
point of view, the snapshot always contains a full copy of the source volumes at the
time it was created.
The supported integrations of arrays with Application Recovery Manager enable you
to create the following types of snapshots:
• Standard snapshot (also known as “pre-allocated snapshot”, “fully-allocated
snapshot”, or simply “snapshot”), where enough space is allocated when the
snapshot is created to hold a full copy of all the source data.
• Vsnap (also known as “virtually capacity-free snapshot”, or “demand-allocated
snapshot”), where no space is pre-allocated.
• Snapclone, which starts as a standard snapshot but where data is copied as a
background task until the snapclone is a complete physical copy of the source
volumes at the time it was created.
These are described below in more detail.
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