Re: Hot Backups

From: Don Vick <dvick_at_lanier.com>
Date: 1995/04/18
Message-ID: <D78GMr.1yL_at_lanier.com>#1/1

In article <3mvatq$bmt_at_ionews.ionet.net>, Laurel McGilvery <lmcgilvi_at_ionet.net> wrote:
>We are currently backing up a 30 gig database to optical disk drives
>using a combination of hot and cold backups. Has anyone out there run
>hot backups backing up more than one tablespace at a time? I know the
>book recommends against it. Just curious what would happen. I don't
>propose testing it on a production system. Our main issue is the backup
>software is NOT as flexible as one would like. Unfortunately, I have to
>use it to access the optical drives.
>

We are wrestling with similar backup needs, and have been frustrated by the capabilities of the backup software. If I understand this correctly, the problem with doing hot backups on multiple tablespaces is redo log limitations. When a tablespace is in backup status, Oracle saves all update activity in the redo logs and catches up the data files after the backup is done. Redo logs cannot be archived if they contain active data, so you run the risk of running out of online redo logs and stalling your system (i.e., blocking udpates). (I may have some details wrong here, but that is the general idea. :-)

Scheduling the backups during light activity may avoid this problem, but if your shop is like ours, finding a period of light activity long enough for a backup is quite a challenge. We are leaning toward a "one tablespace at a time" strategy, even though disk performance characteristics suggest that "one disk at a time" is faster overall.

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Donald E. Vick (dvick_at_lanier.com, dvick_at_crl.com) Voice: (404) 493-2194 Fax: (404) 493-2399 Received on Tue Apr 18 1995 - 00:00:00 CEST