Re: Dual tape drives: logical log and level 0

Allen Jantzen wrote: > On Wed, 25 Nov 1998 17:00:02 -0500, "Art S. Kagel" > <kagel@bloomberg.net> wrote: > >You stop the continuous log backup when you start the archive and > >change the tape, restarting the continuous log backup when the archive > >completes. The archive will backup any logs created in the interrum. > >You just have to make sure you have enough log file space that the logs > >will not completely fill during a typical archive. > >Art S. Kagel > Because I only had 1 DAT drive available at the time, I used this > single-drive approach as you describe. Now, even though I have more > tape drives around, I still use only one drive... > > If you are continuing to backup logical logs while you do an archive, > you have to be very careful about labeling your tapes so that you know > exactly which logical log tapes you will need to do a restore. It > seems that if you do use 2 drives, you are physically and logically > separating the archives from the logical logs.. > By using only a single tape drive, I can just bundle the > last-completed archive tape together w/ the log tape(s) that I just > stopped continuous backup to, and I know that that little > rubber-banded bundle will give me a complete restore. I alternate > thru 5 of these bundles. > Does this make sense to take this approach? > This brings up another point - If the most recent archive comes up bad > during a restore, I can go back to the prior bundle, restore that > archive, and then restore logical logs from that one plus the most > recent bundle. But if a logical log backup is bad, then i'm out of > luck (because they are cumulative). I might get my database back up, > but w/o all current data/transactions. > So it is *much* more important (relatively speaking) to get the > logical log backup right. There are no second chances > there.........correct? Yes to all you say. This is why even when using two tape drives it is important to stop ontape -c and change logtapes immediately before (or concurrent with) beginning the archive. Then you know which tapes you need to get the previous archive restored to the point of the new archive and which tapes you can get rid of after the third or fourth archive is in the can. Your concern about trashed log tapes is one reason why schemes that archive logical log files to disk as individual files that are then backed up to tape by the system archives are becoming popular. These schemes, like those implemented by the Informix eventalarm script, log_full.sh, using onbar, and by my utils3_ak package using ontape, give you additional granularity to your recovery and also give you the opportunity to back up the log archive files to several copies of the system backups before deleting the online versions of the files for extra peace of mind. Art S. Kagel