Design Considerations; Link Sizing - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

Design Considerations

Because every enterprise backup environment is different, there is no single answer for optimizing
replication. This section discusses replication design considerations to help you optimize replication
in your environment.

Link Sizing

Knowing the rate of change of data on your systems and hence being able to size the replication link
efficiently is the key to a successful implementation. Size the link too small and you cannot off-site all
your data in a reasonable time. Size the link too big and you are paying for bandwidth you may not
be able to use. The most likely implementation scenario is either to utilize unused bandwidth in an
existing link or to provision a bandwidth increase on an existing link to accommodate virtual tape
replication. For most users somewhere between a 2 Mb/sec and 50 Mb/sec link should be sufficient
for the amounts of typically data transferred using HP D2D replication. This section focuses on
understanding how to size the replication link bandwidth required.
The size of the replication link will depend on the usage model for replication.
• Backup and replication take place in a fixed window (up to 12 hours) preferably when the WAN
link is not heavily used by applications (i.e., outside business hours). The replication process has
almost the full bandwidth of the WAN link available to it. Within the HP D2D Backup System
configuration for replication you can set a "blackout window" during which time replication is
NOT allowed to operate.
• The business runs 24x7 and there are no fixed windows in which to do replication. In this example
the replication can be limited and the HP D2D devices can be configured to only us a percentage
of the available bandwidth so as not to adversely affect application performance. The replication
will take longer using WAN link throttling.
HP also provides at Backup Sizing Tool to help you size any backup solution including deduplication
and replication:
Sizing the bandwidth required is best illustrated by some examples:
• 100 GB virtual cartridge replication over a 2 Mb/sec link with 100% bandwidth utilization, data
off-sited in a 12 hour fixed window.
• 100 GB virtual cartridge replication over a 2 Mb/sec link with 25% bandwidth utilization, data
off-sited over 24 hours.
• 500 GB virtual cartridge replication over a 2 Mbit/sec link, data off-sited in a 12 hour fixed
window.
• 500 GB virtual cartridge replication over a 10 Mbit/sec link with 20% bandwidth utilization, data
off-sited over 24 hours.
• Many-to-one example with mixed WAN speeds.
84 D2D Systems
http://www.hp.com/go/storageworks/sizer .