Differential Backup question

[zoeythecat]

Hi all,

Question in regards to how directories get backed up in a differential backup versus Full backup. Actually, 2 questions.

(1) The way I understand Differential is that whatever is changed since the last backup will get backed up. What if I have a directory getting backed up just in the differential backup job, but not the full system backup? what happens then?
(2) A recap of question one. I was backing up a directory in both the differential backup and the full system backup. Because we were going over our 35GIG limit I removed this directory from the full backup but kept this in the differential backup. Will this directory still get backed up?

Thanks in advance.

Zoe

 

[Andronium]

Differentials backup everything that has changed since the last FULL backup. Incrementals backup everything that has changed since the last backup of any kind. It could be a little risky to have a directory only being backed up in a differential job. Any file in that directory that isn't changing on a regular basis isn't going to get backed up at all. It would be a good idea to have your full and differentials use the same "selection list name" in the job definition. Why do you only have a 35GB limit?

 

[zoeythecat]

Andronium,

Thanks for the response. We have a 35GIG internal drive so we can only backup to 35GIG. We did not believe at the time that we would reach this limit so we are looking into removing some folders from our full backup. We run a differential on Mon, Tue, Thurs, Fri and full backup on Wednesday. I assume that anything that changes on those days will get backed up though right? Just concerned about being able to restore files.

Zoe

 

[SQLBill]

Zoe,

Yes, your differentials are backing up the changes, however...on Wednesday you do a full back up, Thursday's differential backs up all changes since Wednesday' full backup. Friday's differential backs up all changes since Wednesday (this includes the changes already backed up on Thursday's differential). Monday's differential backs all changes since Wednesday. Etc.

So based on your strategy, if you had to restore on a Friday, you would first restore Wednesday's Full Backup and then Thursday's Differential (unless Friday's had run before the crash).

If you had to restore on a Monday, you would need Wed's full backup and either Friday's or Monday's (if it had finished) differential.

-SQLBill

 

[zoeythecat]

Sqlbill,

Thanks. That helps me understand much better.

Zoe

 

[blonde]

as I understand this, You do a full backup, then anything that is changed will get picked up on the differential. example if the full is done on Monday, anything changed on tuesday will be on the backup of tuesday. anything changed on Wednesday, the wednesday differential will pickup the changes from tuesday & wednesday and so on. If you need to do a restore, it would be from the last full backup and then the last Differential. But if you do incrementals instead of Differentials. then only the changes of that day would be picked up on the incrementals. that may save you space. Only problem is if a restore has to be done, you go back to the last full, and then have to do a restore from all the incrementals up to the date that you need. so you may have a lot of incremental restores that would have to be done in order. but I would for sure do the full backups.
Blonde