Re: DBA FAQ 1 - integrating Backup Strategies

In article <1993Sep2.154509.7195_at_lmpsbbs.comm.mot.com>, cds016_at_isadmin1.comm.mot.com (David Schmitt) writes:
> In article <X5779B2w164w_at_cellar.org>, Scott Tiger <kml_at_cellar.org> wrote:
> >DBA FAQ
> >(Frequently Asked Questions for/from Database Administrators)
> >by Kevin M. Loney, aka kml_at_cellar.org (username "Scott Tiger")
> >
> >3. The Hot Backup.
> >===================
> >
> >Backup strategy for Archivelogs:
> >--------------------------------
.
stuff deleted
.
> >3. Don't do it during user activity. When in backup state, a tablespace's
> >activity is still written to the archive logs. However, it's written
> >block-by-block rather than byte-by-byte. So changing one record in a
> >tablespace that's being backed up will result in that record's entire
> >block being written to the archive area.
> >NOTE: This is correct only for those platforms where the physical sector
> >size is less than the Oracle logical block size. On systems where the
> >physical disk transfer size is equal to the Oracle block size, then we
> >do not incur the penalty of having to log the entire block. This is true
> >for MVS, VM, and perhaps other systems.
>
> Wow. Is this in any of Oracle's normal documentation? Sounds like this
> would apply to us on a UNIX platform.
>
> One of the reasons we liked the idea of hot backups is that we can continue
> batch processing at night. This makes that a little less attractive.

Dave,

Note that Kevin is talking about backing up the archive logs not the datafiles. Datafiles are not a problem as they are backup using a 'fuzzy' copy of the data. The archive logs is a different issue all together.

If you use 'find' and then pipe it to 'tar' or 'cpio' then it is not going to be a problem. This is because by the time the 'find' finishes, any archive log that was being written while the 'find' was going on would (should) have finished. But if you are using something like 'dump', then yes it COULD be a problem. We (Colonial Mutual) have been using hot backups with dump for over 3 years and have not come across any troubles even with the backups carried out during the day.

One technique we use to backup an active filesystems is to pipe all file to a program that checks to see if the files are active ie being open or is being updated. If not it prints the name and if it is, it omits the file name. So you backup only static files.

ta
tony

--
 _____       ________ / ____ |Tony Jambu, Database Administrator
  /_  _        /_ __ /       |Colonial Mutual Invest Mgmt,Aust (ACN004021809)
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