Example 1: 100 Gb Virtual Cartridge Replication Over A 2 Mb/Sec Link With; Bandwidth Utilization - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

Figure 32 Example 1: 100 GB Virtual Cartridge Replication over a 2 Mb/sec Link with 100% Bandwidth
Utilization
.
Calculating data to replicate:
• 100 GB daily backup to replicate within a 12–hour fixed window (between 20:00 and 08:00).
• 1% daily change rate = 0.66 GB compressed
• Overhead (manifest, imperfect match, etc.) is 1.5% = 1.5 GB
• Total data to transmit is 2.16 GB
Result:
• Initial 100 GB backup complete in 30 minutes.
• Replication time for 2.16 GB is 3.46 hours over this link at 100% bandwidth utilization.
The above example shows a 100 GB tape to replicate daily between sites with a Symmetric Digital
Subscriber link (SDSL) between the two sites.
There are several factors involved in sizing the link:
• Full backup size in this example is 100 GB.
• Daily rate of change of data at primary site, in this example 1%.
• Replication required in fixed window or in shared bandwidth mode using bandwidth limiting
(throttling).
• New data being replicated is compressed, communication overhead data (manifest and imperfect
hash code matches) are already compressed.
• Communication overheads typically add up to about 1.5% of the full backup capacity.
• WAN links are not 100% efficient because of TCP/IP overheads contention and so on. This example
assumes 66% link efficiency (typical).
The net result is that the system can replicate a total of 2.16 GB in 3.64 hours with full bandwidth
available at 66% efficiency.
To replicate in shared bandwidth mode, perhaps because this business is a 24x7 operation, then set
the D2D device up to use no more than 25% of the bandwidth available. In this case the replication
will take 14.4 hours which is acceptable to most businesses.
HP StorageWorks VLS and D2D Solutions Guide 85