RE: MS SQL hasn't given up!

no problem Rich. the transaction log mirroring can be done by the DBMS. and SQueal Server has disk devices much like a tablespace that can be placed on different disks and such. transaction logs are kind of like tables in that they must be placed in a device. so yes, these mirrored transaction logs can be kept apart and "safe".

Rachel's comment is also accurate however. if things go way wrong (usually happens to a novice dba) the transaction log can get stuffed so full that there's no way to "archive" it and you end up "truncating" it. users tend not to like it when they can't do DML ;-) anyway, once a transaction log has been truncated there is no transaction recovery until the next database backup completes. and yes - the database backup utility does hot backups.

> -----Original Message-----
> From: Jesse, Rich [SMTP:Rich.Jesse_at_qtiworld.com]
> Sent: Friday, February 28, 2003 1:47 PM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: MS SQL hasn't given up!
>
> Steve, when you say "mirror" are the writes duplicated from SQueaL Server
> or
> hardware? My DBA instructor had distributed some e-mails from a student
> who
> left the mirroring of redos up to hardware. One controller firmware patch
> is all it took to corrupt both copies of the redos.
>
> So, if the mirror is done at the hardware level, it wouldn't be the same
> as
> Oracle. Also, if the TX logs are in the DB, how separated can the mirrors
> be?
>
> Hope this isn't getting too off-topic. I just want to make sure that I'm
> not burning any bridges by refusing to let SQueaL Server get any more DBs
> here...
>
> Thx!
> Rich
>
>
> Rich Jesse System/Database Administrator
> rich.jesse_at_qtiworld.com Quad/Tech International, Sussex, WI USA
>
>
> -----Original Message-----
> Sent: Friday, February 28, 2003 1:19 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Rich - on your first point - that's why you would choose to mirror the
> transaction log in SQeal Server. Same effect.
>
> the transaction log is a fixed size. it can be extended while the db is
> online. but shrinking it is quite a bother (at least was back in the day
> -
> it's been a while). if the transaction log fills up all DML stops.
> database still recoverable though. just need to clean out or extend the
> log
> and all is well again.
>
> no snapshot too old errors though ;-)
>
> > -----Original Message-----
> > From: Jesse, Rich [SMTP:Rich.Jesse_at_qtiworld.com]
> > Sent: Friday, February 28, 2003 12:14 PM
> > To: Multiple recipients of list ORACLE-L
> > Subject: RE: MS SQL hasn't given up!
> >
> > Yes and no. If your logs are backed up every 30 minutes, then you are
> > effectively saying that you are willing to lose up to 30 minutes of
> > transactions, in the event of failure on the TX logs (e.g. hardware).
> > OTOH,
> > Oracle can easily be made to be completely recoverable up to the last
> > transaction ("no data lost") by duplicating, triplicating, etc. both the
> > online redos and the archives.
> >
> > Also, isn't the transaction log area in SQueaL Server in the DB itself
> and
> > at a fixed size (as opposed to Oracle, where you can add redo groups
> > on-the-fly)? In other words, if it fills up, what happens? Does it get
> > overwritten or does the DB continue in an unrecoverable mode?
> >
> > Trying to understand more of this wonderful Enterprise product...
> >
> > Rich
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Jesse, Rich
> INET: Rich.Jesse_at_qtiworld.com
>
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  INET: sollig_at_lifetouch.com

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