Re: Informix backup/archives

In article <343E27B2.2FFC@bloomberg.com>, "Art S. Kagel" <kagel@bloomberg.com> writes >Allen Jantzen wrote: >> Is it a true statement that I will never need any logical log tapes >> that were written *before* my last level 0 archive? In other words, >> when I do a level 0 archive, I am getting essentially a snapshot of >> my database right then, so any logical log tapes made *before* then >> are no longer needed. Correct??? > >Correct. > >> It looks as if the "ontape -c" logical log backup process and the >> "ontape -s -L 0" archive process are completely unaware and completely >> independent of each other. When I stop my ontape -c process and let >> a few logical logs build up on disk not backed up, and then I do a >> level 0 archive, then those logical logs that are sitting there not >> backed up are not really needed anymore (I think). But yet those same >> logical logs will not get reused until I back them up. Why do I have >> to back them up if I don't need them anymore??? Shouldn't the level 0 >> archive somehow flag those logical logs as no longer being relevant, >> so that the space can get reused?? > >You need them in case you have to go to an older archive. Suppose the Or the archive fails to complete e.g. power failure when all of the archive except 1 tape block has been written to tape. Since you need them until the last byte of the level 0 archive is confirmed on the tape and you need them from that point onwards (to handle rollforward if something gets logged the second after the archive completes) there may be less than second window where you do not need the logical logging to tape!!! >media is damaged after the archive is complete and you need to restore. >With the 'out of date' logs you can use your older archive and the logs >to get back up-to-date. It will take time but it will work. > >> If I do a restore from the same level 0 archive mentioned in the last >> paragraph (without restarting ontape -c), will ontape be smart enough >> to roll forward the logical logs stored on disk that haven't been >> backed up yet? Or will it only roll forward from tape??? > >Only from tape. > >BTW and FYI I recently did a warm restore from an Archive taken on one >machine to its sister machine. It worked great! One caviat: you cannot >safely roll forward the logs when you do this because the logs on the >two machines are unlikely to be identical and you may do more harm than >good and if the log numbers are different then ontape will refuse to do >it. The dbspaces restored are left marked inconsistent but Informix >Support can mark them up and they will actually be consistent just not >up-to-date beyond the start of the archive. > >Art S. Kagel -- David Williams