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Taking Differential Backups


#1

Hi guys,

I have a question about taking differential backups; does SSMS needs access to the actual full backup .bak file in order to perform a full differential backup?


#2

No, not for taking the backup. The information is in the system tables.

To restore using the differential backup, you will of course, need the last full backup.


#3

No. Extent maps within the db "tell" SQL which extents have changed so that it can do the differential backup. The last full backup is irrelevant to that process.


#4

ok great, phew.... thanks guys!!


#5

Beware if something/somebody else takes a FULL backup then your Differential backup will be based on THAT OTHER Full backup ... this can be a problem when you come to Restore if you do not have access to the Full backup that preceded the Differential.

We've just had a situation where a Client's outsourced IT support company changed and they "well meaning" (Ha!Ha!) implemented a daily Full and Log backup which broke our Differential and TLog backup chains :frowning: