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Home -> Community -> Usenet -> c.d.o.server -> Re: Redo logs only useful if archiving on
A copy of this was sent to Frank Calfo <TFIAM_at_worldnet.att.net>
(if that email address didn't require changing)
On Thu, 18 Jun 1998 21:05:36 -0700, you wrote:
>Seems to me that the redo logs can only help you recover
>data up to the point of failure if the database is in archive log mode.
>Is that true?
>
NO. they are used for instance recovery from a failure (such as could be caused by a power outage, software failure or shutdown abort).
>Also we have carefully planned our database to place the redo logs
>on separate drives in case of media failure. But again, unless
>we're running in archive log mode, this step doesn't really seem to
>buy us much in terms of data protection. True ?
>
you would have to elaborate on your placement scheme for anyone to answer this question. Do you mean you have multiplexed logfiles on separate devices (>1 member per group, each member on a separate device or do you mean that group 1 is on dev1 and group 2 is on dev2 which affords no protection)....
>(I assume we would still want to consider which drives the redo logs
>are on even without archiving for performance reasons.)
>
The ONLINE redo logs (which by the way should be multi-plexed -- multiple members per group) protect the instance in the event of a SYSTEM crash.
You need the online redo logs to recover the database in the event of a power failure or instance failure.... Make sure you have >1 member per group and that the members of the same groups are on separate physical devices.. That will help in the even of media failure for your log devices.
This step (placing redo logs on separate physical devices) as per your question, buys you the chance to recover from machine/instance failure (but not necessarily MEDIA failure). If you have media failure on one of your data devices and you lose a datafile, then you will have to recover to the last cold backup with no chance of going forward...
>For those of you running in archive log mode, is it working well or
>is it so cumbersome that its not worth the trouble? Would cold-backups
>be sufficient?
It is not cumbersome at all, its pretty easy actually. It is *more then well worth the trouble*. If you can afford to lose data, then you can skip using archive log mode. If you cannot afford to lose data, then archive log mode is the only way to go.
Why do you think it is cumbersome?
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Herndon VA
http://govt.us.oracle.com/ -- downloadable utilities
Anti-Anti Spam Msg: if you want an answer emailed to you, you have to make it easy to get email to you. Any bounced email will be treated the same way i treat SPAM-- I delete it. Received on Thu Jun 18 1998 - 23:50:07 CDT
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