hi team, in my server we will havefull backup on saturday 23.00 and daily differential backup every day at 3.00 am. but these i can find that differential back size is equl to my full backup. what might be the problem help me
Not sure where you setup wrong. I just test on my machine with Diff Backup and size are quite smaller then Full Backup. You can try to run Diff Back Up manually in SSMS and check the size of the backup, you might need to go through your schedule backup again if your manual backup size is smaller then schedule backup.
Differential backup contains all files that have changed since the last FULL backup . These are not incremental.If you are seeing differential backup size eqal to full backup then there must be something wrong. Post output of RESTORE HEADERONLY FROM for each backups.
A differential backup is a backup of all the data pages that have changed since the last full backup. (Well, technically the extents that have changed.) If all the pages have changed, it will be as big as the full backup. Using your backup pattern, I would expect the differentials to start out fairly small and get bigger as the week goes on. But it depends on what happens to the database. As others are suggesting, if you do something like rebuild all the indexes, the differential backup will be as big as the full backup.