Bandwith sizing for SecondSite

The replication product behind SecondSite (Zerto) uses sophisticated data compression algorithms to reduce the bandwidth required between you and Zettagrid. Although this compression is very effective in reducing the bandwidth requirements it is highly dependant on the block changes to disk for each VM being protected by SecondSite. A minimum of 5Mbps of outbound internet is required.

That means we need to identify how many VMs that need protection and then use some sort of tool to determine how large a pipe is needed between you and the Zettagrid zone you would like your DR site in. The file below contains a PDF with instructions on how to determine the required connectivity with two options, one being a manual excel spreadsheet and one being a powershell script that can be run in your environment.

Zerto now also provides Zerto Analytics which includes the Zerto Resource Planner which can provide this information.

WAN Sizing Tool

Please download the WAN sizing tool/s here;

SecondSite WAN Sizing

Networking Scenarios

OK so lets assume initially you do not want to get a link, or you would like to see how things go over the IPSec VPN for a while before committing to a link. Lets go through a few different scenarios to see whether or not the product will still work for your business under different conditions.

Scenario 1

You have 10Mbps available and the WAN sizing tool states you need 8Mbps for the 6 VMs you want protected.

In this scenario you will consistently receive 3-10 second RPOs for all VMs no matter what service profile any of the VPGs have allocated.

Scenario 2

You have 10Mbps in the office and the WAN sizing tool states you need 8Mbps but during business hours the link is saturated and there is only 2Mbps actually available. Overnight though the link is unutilised and has the full 10Mbps available.

In this scenario at the beginning of the day the VMs will have a very low RPO but as the link is saturated during business hours then progressively throughout the day the RPOs of the different VPGs will blow out to about 10 hours at the end of the day. Overnight though the data will traverse the VPN and then the next day again the RPOs for every VM will be as low as 3 seconds.

Scenario 3

You have 20Mbps available and the WAN sizing tool states you need 15Mbps. It is a shared link so it is also used by other services and at times there is only 10Mbps available. Half the VMs are in a VPG with a Gold service profile and the other half are in a few different Bronze service profiles.

In this scenario, generally speaking the VPGs will all have an RPO of a few seconds. At times though when there is not the required 15Mbps available the VMs in the Bronze VPGs will start to have their RPOs increase to a few mins to an hour whilst the VMs in the Gold service profile VPGs remain at an RPO of a few seconds.

Scenario 4

You have 11Mbps available but the WAN sizing tool states you need at least 20Mbps. There is never any stage where there is 20Mbps of bandwidth.

In this scenario you will need to lower the amount of VMs you wish to protect such that the WAN sizing tool reports a number less than 11Mbps or make available enough bandwidth via an additional link or removing other services that may be utilising the bandwidth.