Re: Dual tape drives: logical log and level 0

John C White wrote: > I'm a novice to the DBA task, but the only technically oriented person > around. Which means I'm elected to -specify- as well as administer the > beast. > I'm in the process of specifying the storage and backup sections of > our incoming Online Workgroup Server (7.2). Our DB sizing estimates > indicate that we'll be in the 10-15GB range. We're purchasing a > minimally configured 35GB external hardware RAID. > Question 1: > Is using an external RAID compatible or incompatible with using raw > file space? Compatible but depending on your system you may need a third party volume manager (like Veritas VM) to take best advantage of it. > One thing I've read just recently is the preference to have two tape > drives: one for continuous backup of logical logs, and one for level > 0, 1, and 2 backups of the database proper. We peak out at 4000 lines > per day in our OLTP application. > Question 2a: > How should I size a tape drive for the logical logs vs. a tape drive > for level 0 backups of the DB? > My preference is to have a continuous logical log backups, with one > tape per day for this purpose. I'd also like to run a level 0 backup > once per day. My bias is toward DLT. I was considering the DLT 7000, > as it would be able to handle a level 0 backup of our entire 35GB > uncompressed, were the DB to grow to that size. However, the DLT 4000 > can handle 20GB uncompressed, which would be 33%-100% growth. Not too > shabby. In the time that it takes us to grow that much, I have a > feeling that the DLT 7000 price will come down (right now, we can > purchase two DLT 4000's for less than the cost of a single DLT 7000). > Question 2b: > What is the size ratio of the logical log size to the database size > for a 24 hour period? Less than 75%? Less than 50%? Less than10%? Inserts and deletes require logspace for the row plus header info, updates need logspace for pre and post images plus headers for each and various system conditions, from extent allocation to transaction delimiter records, require log records to be written. It is very hard to judge. > Is buying a DLT 4000 going to be overkill for continuous backups of > the logical logs? DLT is the fastest as safest technology out there today and will guarantee that your logtape does not fill up before you can change it. > Question 3: > > What is best practice as far as grouping database archive tapes and > logical log archive tapes? To paraphrase a song "any plan is a good plan" yours seems to work. > In my mind, I want to synchronize the backups so that the level 0 > archive on tape a0 plus the logs on tape l0 results in the database on > tape a1. Is that how DBA's tend to run things? If ontape -c is a > continuous process, how does one force this condition, especially with > on-line backups? 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