HP P6000 Replication Solutions Manager User Guide (T3680-96089, October 2012)

• Can I create a snapshot of a snapclone?
Yes.
• Can I create an snapshot of a snapshot?
No.
Snapshot types (allocation policy)
Snapshot types (allocation policy) specifies how the storage system allocates space in a disk group
for a snapshot. Values are:
• Demand allocated. The space reserved for the snapshot can automatically change from an
initial minimum amount, up to the full capacity of the original virtual disk.
• Fully allocated. The space reserved for the snapshot is initially set to, and remains fixed at,
the full capacity of the source virtual disk.
When selecting a snapshot type, one consideration is the lifetime of the snapshot and the amount
of source data that will change during its lifetime.
Recommended
snapshot type
Estimated changes
in source data
Snapshot
lifetime
Demand allocatedLess than 25%Short
Fully allocated25% or moreLong
Demand-allocated snapshots
When a snapshot is demand allocated, the storage system allocates only enough space to store
metadata and pointers to the source data. As the source is overwritten, the array allocates more
space and copies the original data to the snapshot. If all the original data on the source is
over-written, the controller increases the allocated space on the snapshot to the full size of the
source.
The size of the disk group in which the source and snapshot are located must be sufficient to handle
increases in snapshot size, whenever the increases might occur. Insufficient space in the disk group
can not only prevent the controller from increasing the space allocation, but it can also prevent
writes to both the source and snapshot.
Fully allocated snapshots
When a snapshot is fully allocated, the storage system allocates only enough space to store
metadata and pointers to the source data, but reserves space equal to the capacity of the source
virtual disk. As the source is overwritten, the array allocates more space and copies the original
data to the snapshot.
Once created, a fully allocated snapshot cannot run out of space.
Types (components)
The type property indicates the component structure of the host volume. This varies with the host
operating system and logical volume manager. Examples:
Device. All OSs.
Logical volume. AIX, HP-UX, Linux, Solaris, Tru64 UNIX.
Partition (slice). AIX, HP-UX, Linux, Solaris, Windows. See Partitions and slices.
Volume set, dynamic disk, spanned volume. Windows
Host volume concepts 137