Re: Rman/Legato/Architecture

  • From: Fuad Arshad <fuadar@xxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Thu, 10 Jun 2004 12:12:15 -0700 (PDT)

but lets say legato has the resources to mount extra tape on extra tape drives.
by alloocating channel rman tries to get channel of the same tape drive becuase 
that is the one is backed onto  unless rman issues a call to getthat tape drive 
legato cannot   mount nor read it.
The only way i see to give rman a specific backup piece and then let it go 
after that particular tape.
we can already get the tape numbers from the rman catalog .
and looking at the documentation the restore command doesnt support  a 
backuppiece restore as of 9i . on the other hand . 
The only possible solution i see is correlatint the datafiles to the backup 
pieces in the catalog and then correlating the  backup pieces to the  tape 
number and creating  scripts during a restore to get the datafiles for  a 
particular backup peice and restore them.
this way i can force rman to call all the tapes at once and thus forcing legato 
to get all the tapes mounted

Byron Pearce <pearceb@xxxxxxxxxx> wrote:

My understanding (not being an expert on the internals of either RMAN or 
Legato) is that RMAN would issue the call for the file that it wants and "pass" 
that request to Legato through an API.  Legato then handles how to process the 
request in order to return the file.  My guess is that the requests would be in 
queue inside Legato waiting for it to manage the restore process.  So, again, 
my guess is that Legato would be the bottleneck.  In my experience I have seen 
it do the same thing from command-line, GUI interface, and RMAN restores.

If RMAN is requesting all of the files on a single tape each time it "passes" a 
file to Legato, then only a single stream would be able to be used no matter 
how many channels you have.  Consider an example where you have 8 files (file1 
- file8).  Now, let's assume for the sake of simplicity that file1 - file4 are 
on tape1 and file5 - file8 are on tape2.  When RMAN requests its files, it asks 
for file1 - file4.  Legato has an index that tells it where all of those files 
are, and they are all on tape1.  Therefore, he cannot use multiple streams 
since he is going to be fast-forwarding and rewinding the tape to get the 
necessary files.  I admit this is conjecture on my part but is consistent based 
on what I have seen Legato do when I last used it (newer versions may behave 

The only way we got it to work was to "trick" Legato into thinking that it was 
running completely separate restore jobs (each with all files on a completely 
separate tape) simultaneously.  In theory, that is the way that RMAN should 
work for each channel but I cannot comment on that conclusively.

Fuad Arshad wrote:
Thanks for the response.
we finally did get  the backups to multiple tape drive
the isue with legato is by default it does 10 streams /tape and a stream is 
basically  a channel in rman.
so we were able to bump the legato streams parameter down to get stuff working 
still figuring  out  how to restore from multiple tapes at a time if you could 
by any chance find the script of your that would be great.
the issue is would it be an rman bottleneck or  a legato bottleneck. becuase 
theoretically if rman  issues a call for a tape and the tape drive is avialble 
loegato should mount that tape. but then how does rman determine what streams 
it wants to get and how can we forceit to use multiple tape drives(meaning  
more tapes than it initally backed up on at  a time.)
How does rman internally determine the streams it wants first .

Byron Pearce <pearceb@xxxxxxxxxx> wrote:

One of the problems that I always ran into with Legato was that it would 
backup to multiple tapes, but that it would restore from a single tape 
at a time. It has been several years since I have worked with the 
product, so that might have changed.

Having said that, we did get it to use multiple tape drives during a 
restore process by having a shell script that would parse the Legato 
database. I believe that I may have those in a tar/gzip archive 
somewhere on another system. It required us to get the various SSID's 
on the distinct tapes and build a shell script for each one. It was not 
a simple process, though once we had it scripted and documented it did 
go rather smoothly. If I can find then, then I will send them your way 
- maybe they will be helpful.

The short answer is "yes" you can do that, but it takes som e work to set 
it up.

Someone else might have a better idea if the newer versions of Legato 
have a simpler way to get around this problem.


Fuad Arshad wrote:

> Got a Questions for all the folks using rman out there.
> We are using rman with a legato networker solution.
> Now after tuning rman like stting up maxopenfiles, setting the 
> filesperset doingg work on the maxblocksize.
> we have tuned the backup about 2Tb to run in 6-8 hours.
> The backup gets 4 tapes and in total writes to 7 tapes.
> the restore took us about 32 hrs which offcourse management didnt like.
> one of the ideas pooped around was .
> Is it possible to allocate more tape drives at restore time
> e.g 4 tapes drive on backup but 7 on restore
> and if we allocate enough extra channels will rman pick up the extra 
> 3 tapes since it did backup on a total of 7 tapes.
> this could cut the rersto re time a lot and i'm trying to get some 
> test environment to try to test this but anyone out face this issue if 
> so how did they resolve/fight thru this
> Thanks

Byron Pearce mailto:pearceb@xxxxxxxxxx
Tenure Systems, Inc. Dallas/Fort Worth, TX

"It's hard to be a ninja when you wear a beeper."

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-- ====================================================================Byron 
Pearce                         mailto:pearceb@xxxxxxxxxxxxxxxx Systems, Inc.    
             Dallas/Fort Worth, TX"It's hard to be a ninja when you wear a 

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