Maximizing Efficiency Through Data Replication Manager Data Movement Application Notes

Data Distribution
Application Notes - Maximizing Efficiency Through Data Replication Manager Data Movement 9
Considerations to keep in mind when using a tape backup solution with DRM are:
• Compaq recommends that backups be performed only at the target site.
• The solution must allow the host with the backup utility full access to the LUNs through both
paths. This ensures the utility will survive a single-path failure. If an operations manager wanted to
perform a backup in spite of an initiator or target site failure, then two tape subsystems are required
(one for each site).
• A snapshot LUN, if used, is read-only. This means that an incremental backup cannot date-stamp
the files, so the backup utility must keep track of the date last backed up in a separate log file. In
the case of exclusive full backups, or when the backup utility keeps backup logs in a database, this
is not an issue.
Data Distribution
Information that companies need to widely disseminate often cannot be tied to one server or location
without causing bottlenecks. To prevent the frustration of trying to access a busy site, this data can be
made available on multiple servers to increase the distribution points (see Figure 6). An example is a
software release where you need the data on multiple servers that are geographically dispersed to
provide wide availability.
Figure 6: Data distribution
To be a benefit, Data Distribution should allow you to make copies of data without slowing down the
main server. This might entail the use of a write history log disk while using SUSPEND and RESUME
commands to prepare the copy during off hours. Write history logging, while good for gathering
initiator updates, requires a considerable amount of time to merge the updates. During this merge time,
the initiator controller may not be able to fully respond to server requests. So, good time utilization of
the server is necessary when using write history logging.
Site A
Site C
Site B
CXO7721A
Originating Site
Note: Data transfer would occur sequentially, and not simultaneously
as depicted.