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

• When can a host read from or write to a snapclone?
A host can immediately read from and write to a snapclone, even during the unsharing process.
• After I create a snapclone, can I delete the source virtual disk?
Yes. However, you cannot delete the source virtual disk until the background unsharing process
is completed. After the snapclone is an independent virtual disk, you can delete the source.
Snapclone guidelines
The following guidelines apply to snapclone virtual disks:
• The array must have a local replication license. See Replication licenses overview.
• A snapclone can be in a different disk group than the source. (A snapclone is created in the
same disk group as its source, unless specified otherwise.)
• The redundancy (Vraid) level of a snapclone can be the same, lower, or higher than the source.
See Redundancy level (Vraid).
• Until a snapclone is normalized, another snapclone of the same source cannot be created.
See Normalization.
Snapclones cannot be created when the disk to be replicated is:
• A snapshot
• A disk that has a snapshot
• In the process of normalizing or being deleted
Snapshots
Snapshot replication of a virtual disk instantly creates a virtual, point-in-time copy of the disk. The
copy is called a snapshot. See also virtual disks Snapshot types and Snapshot FAQ.
The snapshot property indicates whether a virtual disk can be locally replicated using the snapshot
method. Values are:
• Yes. The virtual disk complies with snapshot guidelines. Snapshot replication can be performed.
• No. The virtual disk does not comply with snapshot guidelines. Snapshot replication cannot
be performed.
Preallocated snapshots
Preallocated snapshot refers to a fully allocated snapshot that is created by copying data from a
source virtual disk to a container and immediately converting the container into a virtual disk.
Compared to a standard fully allocated snapshot, creating a preallocated snapshot is faster. In
cases where host I/O must be suspended, the improved speed of preallocated snapshots reduces
the time that a host application is suspended.
When a preallocated snapshot is created, the source virtual disk write cache must be flushed before
replication is started. (See cache policies Write cache.) This ensures that the source virtual disk
and snapclone copy contain identical data. The following table shows how a write cache flush is
implemented.
IMPORTANT: When using jobs or the CLUI, you must explicitly ensure that write caches are
flushed.
Write cache setting after replicationFlush implementationMethod
When replication is complete, the controller
software automatically sets the source disk and
The replication manager automatically sets the
source disk to write-though mode and ensures the
flush has completed before starting the replication.
GUI action
Virtual disk concepts 271