Actually in tests we performed, we have found that there is a point at about
100MB. Below that it seems to not de-multiplex. Above that it does.
Tests that were done was I performed a backup of a multi-gigabyte system
with parallelism set to 4. The Backup was cloned, and the clone was
de-multiplexed. This was different from findings by someone else in the
company, and it transpired they had used small savesets. By trial and error,
we found the point to be about 100MB
Siobhan Ellis
IDATA Integrity Pty Ltd
Sydney
On 17/1/07 7:19 AM, "Patterson, Charles P." <Charles.Patterson AT TUFTS DOT EDU>
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/
> - Any opinions expressed in this message are NOT those of the US Govt. -
>
>
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Siobhán
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