Vendors don’t usually mention that Continuous Data Protection (CDP) replication solutions for remote office servers and PCs that rely on network communication have a major challenge – sending the initial copy of the data to the target environment. It can take weeks, even months, to send the initial full seed copy of the data over a network. After the initial copy has been sent, incrementals can usually be sent overnight with no problems.
Strand explained in the Wikibon Peer Incite held on Nov. 17, 2009 that it took them 11 days to complete the initial data transfers. Stand looked at various options open to them to mitigate the problem:
- Create a mobile (tape or USB-based) copy of the data and ship to the backup site.
- This was not possible because the data was held in block mode on the target Falconstor system.
- Drive or ship the remote FalconStor appliance(s) to the central location, copy the data locally to the backup system, and drive/send the appliances back again.
- This was deemed to be impractical and too risky.
- Put in a short-term high-speed network.
- This was not possible to provide this to the Strand remote locations on a short-term basis.
Using the network was the only way, and this exposed another problem: ensuring that the backup data did not swamp the network and deny communication access to the engineers on site. Denying access would have reduced the productivity of the engineers and delayed engineering projects.
There was a function available on the remote FalconStor CDP appliance to throttle the amount of data that was transferred over the network. However, this had to be set manually. Central IT needed this process to be automatic (there was no remote IT staff to issue these commands), so the IT staff jury-rigged a solution to automatically initiate a script to throttle back communications during the 12-hour weekdays, and allow full speed overnight and weekends. The good news for Strand was that a restart of the backup process was not required at any of the remote sites.
IT practitioners need to remember that sending mobile media such as tape or USB storage devices will often provide higher bandwidth than communication lines!
Action Item: IT shops implementing remote replication software (and individuals using cloud backup software on their PCs) need to calculate exactly how long the initial seeding copy is going to take and find a work-around strategy if necessary. The simplest work-around is a USB-based or other type of transportable storage that can be used to copy the data files locally and then be shipped. IT personnel should include seeding as an important part of the evaluation process for CDP replication solutions.