HP StoreOnce Backup System Concepts and Configuration Guidelines (BB877-90913, November 2013)

StoreOnce VTL and NAS replication overview
The StoreOnce Backup system utilizes a propriety protocol for replication traffic over the Ethernet
ports; this protocol is optimized for deduplication-enabled replication traffic. An item (VTL Cartridge
or NAS file) will be marked ready for replication as soon as it is closed (or the VTL cartridge
returned to its slot). Replication works in a “round robin” process through the libraries and shares
on a StoreOnce Backup system; when it gets to an item that is ready for replication it will start a
replication job for that item assuming there is not already the maximum number of replication jobs
underway. Replication will first exchange metadata information between source and target to
identify the blocks of deduplicated data that are different; it will then synchronize the changes
between the two appliances by transferring the changed blocks or marking blocks for removal at
the target appliance. Replication does trigger housekeeping on the Target Appliance.
Replication will not prevent backup or restore operations from taking place. If an item is re-opened
for further backups or restore, then replication of that item will be paused to be resumed later or
cancelled if the item is changed.
Replication can also be configured to occur at specific times (via configurable blackout windows)
in order to optimize bandwidth usage and not affect other applications that might be sharing the
same WAN link.
VTL and NAS replication is configured between devices using “Mappings” and is not known to
the backup software but is controlled entirely by the StoreOnce appliance. Catalyst Copy is
controlled entirely by the backup software and has no Mappings within the device to configure.
A data import process is necessary to recover data from a target NAS or VTL device, But with
Catalyst no backup application import is required because the additional copies are already known
to the backup software and do not need to be imported.
Replication usage models (VTL and NAS)
There are four main usage models for replication using StoreOnce VTL and NAS devices shown
below.
• Active/Passive – A StoreOnce system at an alternate site is dedicated solely as a target for
replication from a StoreOnce system at a primary location.
• Active/Active – Both StoreOnce systems are backing up local data as well as receiving
replicated data from each other.
• Many-to-One – A target StoreOnce system at a data center is receiving replicated data from
many other StoreOnce systems at other locations.
• N-Way – A collection of StoreOnce systems on several sites are acting as replication targets
for other sites.
The usage model employed will have some bearing on the best practices that can be employed
to provide best performance. The following diagrams show the usage models using VTL device
types.
78 Replication