[Networker] Does cloning unmuliplex and make recovery faster?
2007-01-16 15:09:31
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
SSMC3 4th Floor Rm 4145 | Voice: (301) 713-3284 x210
1315 East West Highway | Fax: (301) 713-3301
Silver Spring, MD 20910-3282 | Web Site: http://www.nodc.noaa.gov/
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