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Looking to make a full backup weekly of a 2008 R2 server which has the OS + a 6TB hard drive with install files, Customer bills, and a couple of other things saved on it/to it.

After that, do incremental or differential backups daily.

At the end of the week, move original and all the inc/diffs over to an offsite machine via internet.

For this example, we would add 30MB per day.

  1. What would be the size of the daily backups (for example Wednesday's diff) individually?
  2. What would be the size of the daily backups (for example Wednesday's inc) individually?

I may not be explaining this correctly, so let me know if something's unclear.

What kind of space would one need to store ALL (full+each day's diff.) backups? Like the full 6TB original backup + monday's diff. + tues diff. + (every day that week)

Would that equal

6TB+30mb+30mb+60mb+120mb+240+480+960+1920= ? Or

6TB+30mb+30mb+30mb+30mb+30mb+30mb+30mb= ?

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2 Answers 2

up vote 1 down vote accepted

An incremental backup gets changes since the last backup of any type (full/incremental/whatever), so the size of the backup should only be the amount of data that has changed since the last backup.

A difference backup will grab changes since the last full backup. So the size on the first backup after the full with only include the changes for that backup. Each following backup is always grabbing what has changed between the current state and the last full. This means that differential backups will require more storage space.

The downside of incremental backups is that you have to restore the last full, and every incremental backup one at a time. So the storage savings comes at the cost of increasing the time it takes to restore.

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With incrementals, you also increase the likelihood of encountering a corrupt backup job or bad media. –  EEAA Jan 26 '12 at 18:01
    
OK thank you. One additional clarification please: What kind of space would one need to store ALL (full+each day's diff.) backups? Like the full 6TB original backup + monday's diff. + tues diff. + (every day that week) Would that equal 6TB+30mb+30mb+60mb+120mb+240+480+960+1920= ? Or 6TB+30mb+30mb+30mb+30mb+30mb+30mb+30mb= ? –  Matt Jan 27 '12 at 22:20

If you're adding 30MB/day, then each day's incremental would be around 30MB.

For differential, the size would start at 30MB for the first diff after the full, and would then increase in size by 30MB each day, until the next full backup at which point the cycle would start over again.

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