Networker

Re: [Networker] tape drive hardware compression a bad thing?

2003-01-29 14:08:07
Subject: Re: [Networker] tape drive hardware compression a bad thing?
From: Bokkelkamp Ernst <ernst.bokkelkamp AT SIEMENS DOT COM>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Wed, 29 Jan 2003 20:07:45 +0100
The funny thing about tape is that is has a finite length ;-)
This means that there is a fixed number of flux changes available, which
means that the number of bits is also a fixed number. The only way to change
the number of bits is to multiply the number of flux changes, which normally
means to increase the number of parallel tracks on the tape. What ever they
do, the number of bits in a certain scheme does not change, it is like a
highway with cars driving bumper to bumper. The only way to increase the
capacity is by adding some more lanes.
But, if we are lucky, and we have a lot of skinny people travelling in the
same direction, then we could cram more people into the cars, which means
that we can transport more bodies while keeping the number of cars constant.
That works well, except if there are a lot of "standard" persons because
that reduces the capacity to the normal rate again.
Now the funny part about all this is that the capacity varies but time
doesn't, it still takes the same time to travel the same distance. This
means that you can increase the quantity if you can deliver the goods, but
you can not vary the time the travel takes ;-)

Bye
Ernie

btw. I love this discussing, brings back lot of memories of the good old
times.


-----Original Message-----
From: Davina Treiber [mailto:treiber AT HOTPOP DOT COM]
Sent: Wednesday, January 29, 2003 7:36 PM
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Subject: Re: [Networker] tape drive hardware compression a bad thing?


On Wed, 29 Jan 2003 12:40:04 -0500, Jim Lane <JLane AT TORONTOHYDRO DOT COM> 
wrote:

>Stan: I'm using DLT7K tapes that are supposed to be 35GB capacity
>uncompressed. when I see, in the "Volumes" display on the GUI, larger
>amounts of data recorded on full volumes, am I entitled to regard that
>as a measure of the effectiveness of compression?

Yes, if the data going to tape is not also software compressed, then the
amount of data written to the tape is indeed an accurate indication of the
effectiveness of hardware compression on that tape.

Save sets that are software compressed show a size much less that the real
amount of data within, so the amount of data on a tape wholly containing
software compressed data should be very close to 35GB.

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