Sql-server – problem creating only differential backups every hour

As with all things in SQL Server, it depends.

First thing you need to do is make sure you understand what each type of backup does.

Books Online has all the gooey details, but here's my summary.

A FULL backup contains everything within the database. A DIFFERENTIAL backup is cumlative NOT incremental. In your example, if your database failed on the 12th, then you'd only need to restore the full backup from the 1st and then the most recent differential on the 12th, then followed by all the transaction log backups upto the failure. A TRANSACTION LOG backup is only needed for databases using the full or bulk-logged recovery model. If you're using the simple recovery model then transaction log backups are not needed.

Now that we've cleared that up...Designing a backup schedule really depends on how much data you need to recovery and how fast you need to recover it in the event of a diaster. I would recommend starting with a full backup each day. You can always reduce the frequency later. Remember the differential backup is cumlative since the last full, so depending on the amount change going on in your database the differential could be larger than the full backup after a few days. If you do a full backup each day, then you may not need to use differentials at all; however you could still do it once a day and schedule it at 12 noon. The transaction log backup only backs up the log. The frequency of the log backup will determine how much data you're willing to lose in the event of a failure. If you run your log backup every 15 minutes, then you would expect to lose up to the last 15 minutes of data that changed. 15 minutes is a good frequency, but every 30 minutes works perfectly for my environment.

As I said earlier, it all depends on your environment. After you've designed and setup your backup schedule, remember to test it on an alternate server. Practice restoring your full, diff, and log backups so that you know everything works like you designed it.

Books Online has some good info if you plan use Maintenance Plans, but if you really want flexibility then check out Ola Hallengren's backup scripts.

There are multiple ways to get to the intended target recovery point with your setup.

A few things:

1. You cannot eliminate log backups for the most important reason of transaction log re-use.
2. It's not possible to know when an issue will occur and thus having multiple ways to get to the RPO is useful and sometimes necessary.
3. Differentials aren't a substitute for log backups, they will lower the RTO as they are much faster to apply than log backups but ultimately aren't worth much on their own (spanning broken lsn points, etc, is useful)
4. How are you going to know which ones you need and don't need ahead of time?

I would not stop taking log backups but you could put into place an aging mechanism in your backup software or process to eliminate files that are no longer needed.

Using your example, you have many paths but the basis is as such:

Always take a tail of the log backup first

1. Restore the full backup, latest differential, all logs.
2. Restore the full backup, all transaction logs.

This is more flexible as a corrupt backup file (say a log file) could be spanned by a differential or a corrupt full could be spanned by differentials, etc.

I would not change how your strategy is currently, but I would make sure it meets your RPO and RTO requirements.