Networker

[Networker] Dumb question on cloning

2010-04-29 15:17:20
Subject: [Networker] Dumb question on cloning
From: George Sinclair <George.Sinclair AT NOAA DOT GOV>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Thu, 29 Apr 2010 15:15:15 -0400
This is kind of a dumb question, and I'm not sure how best to express it, but I'll try:

If you clone all the save sets on a given tape as:

nsrclone -b 'clone pool' -S -f file

where 'file' contains a list of all the ssids on the tape, and the save sets clone successfully to the target tape, then have you really validated anything?

In other words, let's suppose instead that you cloned maybe half of the save sets using the same method. In this case, because the save sets are interleaved with others that may not be in the list, it's going to have to demultiplex those in order to read them so that it can then write them to the target clone tape, right? In this situation, I can see that NW is actually reading the requested data and writing it to the clone target volume.

BUT, in the first scenario, wherein you specify all the ssids, NW is able to more efficiently clone them because it doesn't have to demultiplex anything, correct? In other words, it can preserve the multiplexing, making the operation more efficient over all, although more data would have to be cloned than in the second scenario. BUT, in this case, is it really reading anything like it does in the second? Just seems that the second scenario would be a more thorough test?

Am I wrong here? Is my understanding skewed?


This came up because I clone certain backups manually (cloning is not enabled for the affected groups), and I what I used to do was to launch a clone command (like the one above) wherein I would clone all the save sets from the tapes that were already full, skipping any that spanned onto appendable volumes, and then level full backups could also run at the same time to those appendable volumes and so on and so forth throughout the week. Finally, once the final fulls were done, I'd then clone those. Obviously, this involved a number of separate clone operations, and each had to clone a subset of the overall save sets, so it was more inefficient than simply waiting until all the fulls were done and then running one clone command for everything as this will better preserve the multiplexing. BUT, in retrospect, I'm wondering if the former method is a better test or validation as it has to demultiplex since it's working on a subset? OR, is running on the whole thing good enough?

Thanks.

George

--
George Sinclair
Voice: (301) 713-3284 x210
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