Re: Informix database backups

>From: uunet!sword.eng.pyramid.com!echen (Eric Chen) >Message-Id: <181355@pyramid.pyramid.com> >Subject: Re: Informix database backups >Date: 30 Apr 92 03:16:23 GMT >X-Informix-List-Id: <news.1141> > > But how about the other performance bottleneck -- the single thread >I/O as done by tbtape to read data off the disk is still there. Did you >guys provide any solution on that for customers ? The typical speed of >reading database off disk is probably 600 - 800 KB/s which means 20 hours >to do 50GB database and I doubt the "commercial customers" still care the >few minutes locking between changing tape reels :-) > >========================================================================== >Eric Chen Database Division, Pyramid Technology echen@pyramid.com >========================================================================== This is completely unofficial, but... It is fair to say that Informix is aware of the problems of backing up really huge databases, and is working on it. The best information I have (without having enquired specially) is that the tape handling system is due for a re-write in Version 6.0. Take that with a pinch of salt -- that is just the next scheduled version -- but it might be there. One of the problems with backing up a huge database to tape is the tape bandwidth -- as well as the disk bandwidth. Even with 50 tapes working in parallel (and 50 disk drives to keep them supplied with data, and 50 parallel tape backup processes scheduling the information transfers), it is going to take time to complete a backup of a 50 GB database. Assume, for sake of argument, that both the disks and the tape can manage 1 MB/s, and the parallelism I have specified does not affect the performance. It is still going to take 1024 seconds to back up the system -- just over 17 minutes. I don't believe many installations can have 50 tape drives attached to a single machine (even if networked devices are allowed for). I don't believe many tape drives and disk drives can sustain 1 MB/s transfer rates simultaneously. That means the estimate of 17 minutes is ridiculously small, but it also shows that it is not reasonable to expect that sort of speed for backing up very large databases. Even straight volume copying (bypassing Informix tape handling completely) will take a long time on that size of database, and there is no guarantee that the data will be consistent, whereas using the Informix utilities do guarantee that. Jonathan Leffler (johnl@obelix.informix.com) #include <disclaimer.h>