Networker

[Networker] Does cloning unmuliplex and make recovery faster?

2007-01-16 15:09:31
Subject: [Networker] Does cloning unmuliplex and make recovery faster?
From: George Sinclair <George.Sinclair AT NOAA DOT GOV>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Tue, 16 Jan 2007 15:00:45 -0500
I recently recovered a 4 GB saveset from a clone backup tape. I was surprised how fast the recover was. At first I thought there was some kind of mistake, but I compared the recovered data to the same data pulled off the original, and everything matched.

I'd made the clone manually ('nsrclone -s server -S -f file', where file contained a list of several ssids from the original source volume). I noticed that the recovery time for the clone was lightning fast, but the recover time for the original, while certainly acceptable, was much slower, and I was already factoring out the time for the tape to position itself. The clone volume is actually an SDLT 1 tape, and was being read on an SDLT 1 drive. The original was an SDLT 2 tape on an SDLT 600 drive. Clearly, the SDLT 1 drive is at a disadvantage.

We have target sessions set to 4 on our devices so typically about 4 save sets get wrapped together on backups. Is it the case that cloning undoes this multiplexing and writes the save sets out individually on the clone, and this is why the clone was so much faster since it didn't have to undo anything? Could there be some other reason?

Thanks.

George

--
George Sinclair - NOAA/NESDIS/National Oceanographic Data Center
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