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Re: Slow RMAN Backups

From: goran bogdanovic <>
Date: Mon, 21 Aug 2006 12:21:56 +0200
Message-ID: <>

Hi Mirza,

Check the size of rman input buffer:
select set_count, device_type, type, filename, buffer_size,

       buffer_count, open_time, close_time   from v$backup_async/sync_io
 order by set_count,type, open_time, close_time;

Monitor input buffers to see how much memory is being allocated and adjust MAXOPENFILES. Check also the the size for the write buffers. The write buffers can be adjusted with BLKSIZE channel parameter. Increasing the buffer can reduce the number of I/O calls to the MML and eventually reduce the amount of I/O time.


On 8/18/06, Naqi Mirza <> wrote:
> Hi,
> I was wondering whether anyone has experienced poor backup times with
> oracle databases on RAID 5? We are using netbackup in conjunction with rman
> to backup a 1.5TB database that takes about 16 hours to complete. A host
> of rman parameters have been tried - combinations of filesperset and
> maxopenfiles - with no benefit seen. Our database uses RAID 5 spread over
> about a 100 disks. We have noticed that no matter what we do the maximum
> throughput for the backup is only 50mb/s. We are using an LTO3 tape library
> which can write at 60mb/s per tape drive. But no matter how many tape drives
> we allocate for use (we use 3 channels - 3 drives) we only get 50mb/s as the
> total throughput - resulting in a backup that is over 16 hours. What happens
> is, if one channel is allocated the throughput for that might be around
> 50mb/s, when a second channel is allocated, the total throughput remains
> around 50mb/s which is distributed over the two channels. Adding a third
> gives no benefit as the 50mb/s throughtput is then distributed over all
> three channels.
> I have monitored v$backup_aysnc_io and have noticed that there is for the
> most part poor read rates as seen by the effective_bytes_per_second for
> TYPE='INPUT'. From that I can only infer that the slower the read done by
> rman the slower the backup will be - I do not see any problem with respect
> to writes to the tape drives - they will write as fast as they recieve data.
> We have seen with a filesystem backup we are able to achieve a rate of about
> 100mb/s - although this type of backup is different to an rman backup there
> is quite a difference seen in the rate. Just wondering if there is someway
> to work out if the RAID configuration could be the issue here and whether
> the diskratio parameter might be a viable option to try.
> Thanks

Received on Mon Aug 21 2006 - 05:21:56 CDT

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