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Re: [Networker] Does cloning unmuliplex and make recovery faster?
2007-01-16 16:04:15
That make sense, and I can see that a clone offers more advantages than
just being an
extra copy and a validation of the original.
I thought, though, that I remember someone once remarking that
multiplexing was preserved
on clones unless you did it manually with nsrclone -s ssid ... Maybe
that was just misinformation.
Just confirming here ... it doesn't matter if cloning is done
automatically (e.g. enabled for the group) or manually?
Also, I assume that cloning will generally take longer than the original
backups because it must undo each saveset
one at a time even given that the network load may not play a factor
during cloning? No wonder cloning is a time expensive venture.
George
Patterson, Charles P. wrote:
Cloning de-multiplexes the data so the clone should always restore
faster than the original (assuming you use target sessions higher than
1).
Also cloning will attempt to keep savesets on one volume whenever
possible. In other words it will reduce volume spanning of savesets as
long as they aren't larger than one tape.
- Charlie
Charlie Patterson
Backup Administrator, Computer Operations
University Information Technology (UIT)
Tufts University
-----Original Message-----
From: EMC NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On
Behalf Of George Sinclair
Sent: Tuesday, January 16, 2007 3:01 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: [Networker] Does cloning unmuliplex and make recovery faster?
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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--
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/
- Any opinions expressed in this message are NOT those of the US Govt. -
To sign off this list, send email to listserv AT listserv.temple DOT edu and type
"signoff networker" in the body of the email. Please write to networker-request
AT listserv.temple DOT edu if you have any problems with this list. You can access the
archives at http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER
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