Example - Calculating SRL size for a VVR configuration

This section shows how to calculate the SRL size for a VVR configuration after you collect the site parameters.

Table: Parameters for calculating the SRL size provides the relevant parameters for SLR size calculations.

Table: Parameters for calculating the SRL size



Application peak write rate

1 gigabyte/hour

Duration of peak

8 am - 8 pm

Application off-peak write rate

250 megabytes/hour

Average write size

2 kilobytes

Number of Secondary sites


Type of RLINK


Synchronization Period:

- application shutdown


- copy data to tape

3 hours

- send tapes to Secondary site

4 hours

- load data

3 hours

- Total

10 hours

Maximum downtime for Secondary node

4 hours

Maximum downtime for network

24 hours

Secondary backup

not used

Because synchronous RLINKs are to be used, the network bandwidth must be sized to handle the peak application write rate to prevent the write latency from growing. Thus, the peak usage constraint is not an issue, and the largest constraint is that the network could be out for 24 hours. The amount of data accumulating in the SRL over this period would be:

(Application peak write rate x Duration of peak) + (Application off-peak write rate x Duration of off peak).

In this case, the calculation would appear as follows:

1 GB/hour x 12 hours+ 1/4 GB/hour x 12 = 15 GB

An adjustment of 25% is made to handle header information. Since the 24-hour downtime is already an extreme case, no additional adjustments are needed to handle other constraints. The result shows that the SRL should be at least 18.75 gigabytes.