Replication Limitations - HP 12000 Design Manual

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 (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 replication 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 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.
Replication 23