Re: RMAN

On Wed, 27 Aug 2008 13:13:46 -0700 (PDT), artmerar_at_yahoo.com wrote:

>Sybrand,
>
>Forgive me for this last question.
>
>I think I understand backupset & backuppiece. Usually each backupset
>is allocated to a different channel.
>
>Filesperset I'll have to do a bit more reading on as to understand why
>3 files writing to 3 different backup sets vs 3 files writing to 1
>backup set makes a difference.
>
>MAXSETSIZE sets the maximum size per backupset, I assume. Would
>setting both filesperset & maxsizeset conflict? I'm trying to think
>about this. If you have 12 files, and you say you want 4 files per
>set, thus 3 sets, and a maxsize of 50G per set.......you may get more
>than 3 sets, defined by the previous filesperset value......
>
>I'm probably wrong.....
>

backupsets are NOT allocated to different channels unless you instruct it do so. Channels are backup destinations, sending subsequent backupsets to different channels doesn't make sense.

Three files written to 1 backupset are three files opened *simultaneously* (by three different Oracle sessions), read in parallel, and written in parallel to 1 backupset.

Rman will calculate the space required, with as guideline a datafile can't span a backupset. If 4 files don't fit in 50 G, RMAN will create extra sets and adjust the number of filesperset automatically.

-- 
Sybrand Bakker
Senior Oracle DBA