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Re: RMAN Performance Maladies

From: Naqi Mirza <>
Date: Mon, 12 Feb 2007 11:14:44 -0800 (PST)
Message-ID: <>


I know one site that has their 4TB database backup in almost 18 hours,
they are on 9.2, using veritas netbackup 5. What are you using by the
way, I seemed to have missed that in the post? You also haven't
mentioned whether your backups are to disk or tape? If tape then which
tape technology. If its LTO and i remember correctly, LTO3 is the
latest and each drive has a maximum rate of 80mb/s, So you may want to
be the math for that and work out what you can achieve - at least with
all things being equal. Which is really a question in itself - are all
drives streaming with data and if so to what extent?. See from what I
have come to understand about rman - you will only be able to write
data to tape at least as fast as you can read it, if you're not reading
fast enough you won't be able to write much either. 

Now, there are two dynamic performance views you can query to obtain
this information. Depending o n how the backup is being
done-v$backup_io and v$backup_aysnc_io (hope thats correct, do check
the oracle reference manual). Have a look at the column -
effective_bytes_per_second with respect to the column type (values here
of INPUT - is what you are reading at, and OUTPUT is what you are
writing at - either to disk or tape). See if you are reading at decent
speed , then check to see if you are writing at least at this rate -
you can also check with your backup software to see the throughput that
is being achieved.

The problem I witnessed at a certain site - never got resolved, the
site was also using RAID 5 - I suspected this as the culprit - however
incompetence on my part, I could never really prove it. A few more
things which you can check - since i did the same. Is see whether a a
file copy of a particular datafile results in the same rate being
achieved by your backup software. The issue we had was that netbackup
would show the total throughput of the backup as 50mb/s no matter what
was done - channel increase, maxopenfiles, filesperset, etc. The
sysadmin at the site claimed that rman was the problem and that o/s
backups would typically give them 100mb/s. I removed rman from the
equation, and had netbackup backup a datafile in backup mode - guess
what it still showed a throughput of 50mb/s - so it wasn't rman and
this is what I believe, alas, to this day.

Do check iostat , during your backup runs - does it reveal any io
contention that could be hindering the backup. Hows your cpu usage
during backups - rman is 'apparently' heavy on the cpu.

One more thing to add to the equation here, I know another site, which
i used as a comparison to the 18 hour site. Comparing the
effective_bytes_per_Second there showed a tremendous difference, they
were reading alot more data and therefore writing more too, thus ,
there 1.5TB database would complete its backup in about 2-3hours
(cannot recall now exactly which).

Well, I have digressed a bit here, hoping perhaps someone might be able
to give me a clue or two too. Hope what I have written gives you a
start - checkout the site - there are a few papers on
there that help you troubleshoot rman performance problems.


----- Original Message ----
From: Michael Fontana <>
Sent: Monday, 12 February, 2007 9:15:22 PM
Subject: RMAN Performance Maladies

We have just implemented RMAN against our largest Siebel implementation
(don't laugh - but it's less then 1/2 terrabyte).
We did so because now that we have upgraded to Oracle 10gR2 (
we can take advantage of flash recovery features and full backup
compression similar to which we achived with our old backup product (BMC
Sqlbacktrack).  We customarily take full backups nightly, as per our
SLA, and at this point, incrementals are not an option.  However, the
actual runtime to complete a full database backup with RMAN compared to
SqlBackTrack has gone from 30 minutes to over 4 1/2 hours!  

I have seen anecdotal reports of long runtimes for full RMAN backups on
this list, but I've seen an overwhelming number of guffaws from the more
elite and experienced poster indicating that this must be user error or
some other database performance problem that any competent DBA should
easily be able to solve without posting to this list.  However, even
after opening an SR with Oracle support, who seems to believe our
runtime is in the expected range, we still believe something can be done
to overcome the huge IO spike and slow performance we are witnessing
during the backup, and we are not that experienced with RMAN from a
performance and tuning perspective, and would appreciated anyone's
insights or experiences.

My question is - has anyone actually run RMAN against a large (> 200g)
database right out of the box without tuning?  

Has anyone spent a great deal of time tuning?

We are running 4 channels, have an 8 cpu Sunsparc solaris with 16g of
memory, and have experimented with recommended parameter settings for
maxsetsize and maxfilesperset without success.  Any information or
assistance or comment would be appreciated, thanks in advance!


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Received on Mon Feb 12 2007 - 13:14:44 CST

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