Measure or estimate the GB per hour rate
It’s helpful to think in GB/hr, not Mbps or Kbps. The best method is to back up about 5GB and see long it takes. The backup log will record the start time, end time, duration and the amount of data protected. otherwise, you can estimate a GB per hour rate with either of these two rules. They are equivalent:
- Expect to move .8GB/hr on a T1 line (1.5Mbps)
- Expect to move .5GB/hr for every 1Mbps of upstream bandwidth
You can scale these numbers up or down based on the amount of bandwidth you actually have.
Estimate the Initial Backup Time for each server
Normally, you will not want the initial backup to be running during business hours without a bandwidth throttle. So don’t plan on the measured or estimated GB/hr rate being available 24 hours a day during weekdays.
Make your plan
A typical plan is to backup the most important servers at a site over the first weekend, and other servers at night or on following weekends until all the servers and data at the site have been protected. (Don’t plan on doing multiple servers at the same time.)
If a server has more than 100GB, plan to create multiple backup policies, with each policy between 100 and 200GB. Do the initial backup for one policy before creating another policy and backing up more data under the new policy.
If a single policy is expected to take more than 2 or 3 days, limit the number of directories or partitions in the policy at first, and let part of the data complete its initial backup before adding the rest. That is, do the initial backup in stages.
Use bandwidth throttles appropriately
A good practice is let an initial backup run over the weekend with no bandwidth throttle. If a server has not completed on Monday morning, create a bandwidth throttle schedule on Monday morning that limits the bandwidth usage during weekday business hours. This way the initial backup will continue during the business day but at a background rate.
Don’t stop your current backup practice right away
You should continue with your current backup practice until the initial backup has completed and a few days of delta backups have occurred. There is no reason to place yourself at risk of having no backup for a period of days.