RE: RMAN question(s)

Hi Robert, could you please clarify a couple things for me since I've never tried compressed backupsets?

1. My understanding is that "as compressed backupset" is not recommended if you're backing up to a tape drive (e.g. LTO3) that is already performing its own compression. Is that correct?
2. You say compression will save time as well, but I thought that a compressed backup would actually take longer due to the extra processing required for the compression. I can't see how it would save time unless you are on a very IO-bound system such that the extra processing time for compression is more than compensated for by the reduction in disk writes (especially if you're backing up to RAID5), or if you are transferring over the network obviously there would be significant time savings from the smaller file to transfer. Do you typically find that the reduction in disk write time outweighs the increased CPU time?

Thanks,
Brandon

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Robert Freeman Sent: Wednesday, August 29, 2007 6:32 AM To: oracle-l_at_freelists.org
Subject: RE: RMAN question(s)

Seems you have already gotten some great answers! I might also suggest, if you are in 10g, that you look at adding compression to your backups (backup as compressed backupset database plus archivelog delete input). You might be amazed at how much smaller your backupsets are and how much time using compression can save on your backups (at the cost of some CPU of course).

When I do RMAN courses I like to demonstrate a compressed vs. non-compressed RMAN backup. The compression itself can be impressive, the time to backup savings can likewise be impressive (Ceteris paribus.... oooops, can I say
that.....?)

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