Post reply

differential backups

  • November 21, 2005 at 9:08 am

    #111398

    A differential backup backs up all extents that have changed since the last full backup. As only changed extents are backed up, the differential backup is usually substantially smaller than a full backup. This is a major factor in allowing SQL Server to scale to Very Large Databases (VLDB).

    My question is what about the small size of differential backups help SQL to scale to vldbs. PLease clarify.

  • November 21, 2005 at 9:18 am

    #604991

    Hi,

     

    Should imagine this is more to do with the time window for backups - and also the amount of storage required to back up VLDB's - if you have a 100 Gb database, and you are carrying out full backups with 1 weeks retention - well you can do the maths. Whereas differential as you say only backs up tye changed data, so on a OLAP DB, this would be negligable - say 1 Gb changed daily - with one full backup weekly would give a backup storage requirement of 100+1+2+3+4+5+6 GB of storage against the 700Gb for nightly full backups (This obviously does not count the transaction log backups). If however you have a OLAP based DB that is carrying out lots of changes against the data, you could actually end up with having as large a backup set as for Nightly Full Backups.

    Hope this helps

     

    Steve

  • November 21, 2005 at 9:51 am

    #604998

    Thanks a lot. Your answer really helped me understand how differential backup help SQL scale.

Viewing 3 posts - 1 through 2 (of 2 total)

You must be logged in to reply to this topic. Login to reply