Forum Discussion

fry-nbu-fla's avatar
7 years ago

Cumulative vs differential backup performance during a restore

I am looking for information regarding the performance of a restore using cumulative incremental vs differential incremental backups.  I understand the difference between the two.  If the full and incremental backups are to a disk based backup system, i.e. a 5230 netbackup appliance, which full and incremental backup combination is better for a restore, cumulative or differential?  I understand in a tape environment that a restore using a cumulative backup will reduce tape mounts but in a disk environment where no tape mount is required, is there a performance improvement when restoring a server using a full and a cumulative incremental backup?  If so, how much better is it over a full and differential backup?  If anyone can share performance data, it would be appreciated.  I am assuming a weekly full and daily incremental backups.

  • X2's avatar
    X2
    Moderator

    No performance comparison data here. However, I would consider the fundamentals in making the decision. (You know this but others searching something similar might benefit) - Differential Incremental (DI) means that you restore from a FULL backup and then all subsequent DI backups till the target date. Hence, the possibility of multiple tape mounts. Cummulative Incremental (CI) means a restore from FULL backup and then from the target date CI backup. So, basically around two mounts of tapes (or more if there image spans multiple tapes).

    Disk based images reduce the mount time and positioning time that tapes require, however, if there is a lot of daily change in your data, the CI backups themselves take a long time to finish as opposed to DI backup.

    You need to consider the type of data too. Is  deduplication involved in the disk storage unit? If yes, data with less deduplication rate will rapidly fill up your disk. Sending that data to tape might be more logical (e.g. encrypted data, video files, etc).

    So, it depends on your environment and RTO requirements.

    PS: I usually go for weekly CI when I'm doing monthly FULLs for large volumes.

    • Thanks, X2.  If Accelerator is thrown into the mix, would that change your thoughts? 

      • Lowell_Palecek's avatar
        Lowell_Palecek
        Level 6

        If you are backing up a database or database application such as Microsoft Exchange or SharePoint, consider that taking cumulative incremental means that the database can't truncate the transaction logs (delete the log files) until the next full backup. I think Exchange users tend to prefer incremental backups because they can have tens of thousands of 1 MB log files generated per week.

        Accelerator does change the picture at least for Exchange. Exchange itself is slow at replaying the logs from an incremental backup. With Accelerator, you may as well take only full backups. Full Accelerator backups take the space of differential backups but restore in a single step.