clarification on parallelism

In the process of answering questions for others, I have triedresearching this and can't determine for sure what the answer is.

In the original presentation of Amandahttp://www.usenix.org/publications/library/proceedings/sa92/silva.pdf(that's actually a pretty cool historical document), it clearly saidthat a backup has to be completed to the holding disk before it wouldthen be run out to tape. It also said that if a backup was too large tofit on the holding disk, it would be streamed to the tape sequentially,after other backups had been completed.

Since then a lot has changed. The size of things that people are dealingwith has gotten much larger, and Amanda can now span tapes.

With that ability to span tapes, does Amanda still require a DLE to becompleted to holding disk before it will send any of it to tape? And,does it still stream sequentially to tape if a DLE is too large for aholding disk? And, what if you are doing server side compression? Is itthe entire DLE that gets compressed in one go? That would certainlyanswer the first question.

I realize that the ultimate answer is that it is better to break upDLE's so that you don't have any so large, thus allowing parallelismfrom, say, a large SAN that in fact has multiple luns and is capable ofparallelism itself. But, knowing how Amanda is going to handle a verylarge DLE does help explain options and tradeoffs.



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Chris Hoogendyk

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  O__  ---- Systems Administrator
 c/ /'_ --- Biology & Geology Departments
(*) \(*) -- 140 Morrill Science Center

~~~~~~~~~~ - University of Massachusetts, Amherst

<hoogendyk AT bio.umass DOT edu>

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Erdös 4