read each tape about 6 times (the parallelism) to make the clones.)

multiplexing (but, of course, for only those save sets).

to tape for our two tape copies.

On 17/01/2007, at 9:06 AM, Siobhán Ellis wrote:

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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