Replication Limitations - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

On a VLS (by default) or a D2D (if you enable the read-only mode on the target library), you can still
present the replication target to a different backup application instance (i.e., a separate backup
application master/cell server on the target site with its own media database), which you can use to
"import" replicated cartridges into its media database and then perform restores or copy to physical
tape, etc. See
"Creating Archive Tapes from the
NOTE:
With HP Data Protector, if you have a cell server in each site that can share library devices across
sites through a MoM/CMMDB, you still need to ensure that each cell server only sees its local virtual
library (i.e., the source cell server must not be configured to see the target virtual library and vice-versa).

Replication Limitations

VLS and D2D replication may not work in every environment. Understand the possible limitations:
• Do not confuse Virtual Tape Library replication with "high availability/continuous access" which
is a type of full bandwidth replication used on Disk Array technology whereby primary application
data can be accessed within hours of a disaster at one site from the other site. Virtual tape replic-
ation is not high availability; it is a means of automating the offsiting of data resulting in better
disaster recovery coverage.
• System data rate change. The higher the data change rate, the more data requires replicating.
Systems with very high change rates and slower links may not be able to replicate all the data
off-site within 24 hours.
• High latency links. For very large distance replications with many routers involved, the latency of
the WAN link may lead to high inefficiency of the link where throughput is limited and replications
cannot be performed in a timely manner.
• Current link speed is too slow or the implementation of replication on the existing link will cause
unacceptable delays in application response times. Using the HP StorageWorks sizer tool and
some of your inputs, you can evaluate if you will need to increase an existing link speed to be
able to benefit from replication. See http://www.hp.com/go/storageworks/sizer.
• Some additional financial investment will be required as increased bandwidth links, hardware
additions, and/or deduplication and replication licenses, but in general the increased robustness
of the data protection process should pay for itself within 2–3 years.
• On the VLS, the HP Accelerated deduplication relies on understanding the metadata format of the
incoming data stream. It does not currently support all data formats and backup API's. In the case
where an HP VLS cannot deduplicate the data type, the data is sent untouched to the VLS. This
data is replicated as "whole cartridge;" the entire tape contents are replicated and not the delta's
or unique data objects. If a high percentage of your date cannot deduplicate, the volume of data
to replicate will be very large. If you do not have very large volumes of data to replicate, you
should consider using HP whole cartridge replication. This works essentially in the same way as
replication using echo copy pools; it requires no tape transfer or initialization and no deduplication
or replication licenses. However, all data is transferred between sites and this means the WAN
links will have to considerably higher performance at an associated higher cost.
"Creating Archive Tapes from the
Target" on page 99 (D2D) for an example on automating this.
Target" on page 190 (VLS) or
HP StorageWorks VLS and D2D Solutions Guide 29