RE: Multiple DAT Drive Backup

Everybody, Is there a reason why Informix doesn't detect for end of tape and then ask for the tape to be changed? The current implementation has always seemed very clumsy to me. I can understand that it would be a more difficult process to write eg: you only write half a page to a tape and then it runs out, but you could just write this page to the new tape. Regards, David Ashby -----Original Message----- From: June Tong [mailto:june_t@hotmail.com] Sent: Friday, 28 August 1998 10:05 To: informix-list@iiug.org Subject: Re: Multiple DAT Drive Backup Paul Wheeler wrote: > We have a secondary DAT device attached to our HP9000 server which is > currently > unused. Is there a possibility of utilising both DAT drives to complete the > backup process > without the requirement of user-intervention to swap the tapes. Hmmm. Well, I'm sure there is, but it would probably be ugly. As you've undoubtedly noticed, there is no where in the config to tell ontape to use two different tape drives. You would have to fool ontape into thinking they were the same drive, possibly by using a link and moving it. So you'd have to write a wrapper that called the ontape program, detected when it prompted for the next tape, moved the link to the second tape drive, and sent the carriage-return to ontape. Actually, I think there are similar wrappers in the IIUG archives which write to disk files; you could modify one for your purposes. Or use tape striping, as someone has mentioned. > Another approach we have thought of is to enable compression on our primary > DAT drive > thereby giving us a maximum 8Gbyte capacity. The issue here is that there > is no guaranteed > compression ratio and therefore the tape capacity is variable. How would > this be specified > in the tape parameters? I'm glad you mentioned this. A lot of people have been bitten by this, not realizing that the stated 8GB is only a maximum, not a guarantee. There is no way to tell ontape about this -- you have to guess, and if you guess too high, ontape will fail when it hits the end of the tape prior to having written as much data as you said it could. If you want to squeeze every last inch out of your DAT tape and have lots of time to kill, you can try starting at 8000000 (MB) and see if it fails, and slowly lower it until you get to a point where it succeeds. Note that because it succeeds today is no guarantee that it will succeed tomorrow. In my experience, most of the time setting it between 7000000 and 7500000 will work. But I do remember one site who, having had it working for weeks at 7000000, spent a lot of time trying to figure out what happened when it suddenly *stopped* working. They eventually had to go to 6500000. June -- june_t@hotmail.com Lost in the wilds of Palo Alto, living on sushi