Networker

Re: [Networker] How to tell how much physical tape is being used?

2007-04-24 16:58:06
Subject: Re: [Networker] How to tell how much physical tape is being used?
From: George Sinclair <George.Sinclair AT NOAA DOT GOV>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Tue, 24 Apr 2007 16:56:53 -0400
Stan Horwitz wrote:
On Apr 24, 2007, at 4:04 PM, George Sinclair wrote:

Excellent point, but if that 10 GB is being compressed down to say 5 GB via the 'compressed' option, for example, then you're only using 5 GB of tape, but if your rman script isn't using the 'compressed' option, and you're sending all 10 GB to the drive then the drive is still gonna use hardware compression, so how do I determine which method actually used less tape? Maybe it's a toss up?

If you are using hardware compression, then using software compression on top of it (for any kind of data, Oracle or other) will give rise to the possibility that the data might actually take up more space on your tapes, not less. Usually, hardware compression is the way to go and software compression should be used only in a narrow set of circumstances such as a situation where a client has a lot of compressible data and a slow network pipe.

Good point, and I agree. It's just that Oracle's compression was so massive that I got to thinking that even if the subsequent hardware compression actually increased that size, the reported backup sizes were on an order of magnitude smaller than when no Oracle compression was used. This got me thinking that the data must be highly compressible even though Oracle's compression was being used. As a result, perhaps not using Oracle's compression and just letting hardware compression handle it might still result in the same level of compression even though the reported backup sizes would be larger.

I think we'll turn off Oracle's compression and just use the built-in hardware compression. I was just curious if there was a way to determine which method actually used more physical tape.

George

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