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Tape capacity dramatically improved with Retro 9?

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I note that in the tapes that I have written so far with Retro 9, the capacity of the tape, as reported by Retrospect, is improved by around 30% versus that reported by Retrospect 6.1.


This could be how the data size is reported, but Retro 6.1 seemed to report the uncompressed data size, and I expect that Retro 9 does the same. (otherwise my numbers make no sense!)


I have a USB HP DDS-5 (DAT72) tape drive, and with Retro 6.1, it was rare for me to get more than a hair better than the "native" data capacity. DDS-4 tapes claim 40 GB, but actually hold about 20 GB uncompressed, and get 40 GB only when compression is maximal. With DAT72 tapes, I would normally get 35 GB. Never more than 37.


With Retro 9, I'm seeing 45, or even over 50 GB on a single DAT72 tape.


Whatever was done, it's good. ;->


(Was the compression broken in 6.1?)


Thanks to Retrospect team.

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Were you running both Retro 6 and 9 on the same hardware?


If "yes":

Since Retro 9 doesn't run on PowerPC, you must be running on an Intel Mac. That means Retro 6 runs under Rosetta, which is a performance penalty. That, in turn, means that Retro 6 couln't feed data to the tape drive fast enough. So the tape drive would either leave blank blocks on the tape or stop and start continously.


If "no":

Your old (?) Retro 6 hardware was probably not fast enough to satisfy the tape drive fully.

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Having no direct knowledge of my drive and how it works internally, I hesitate to comment, but the relative speeds of USB2 (60 MBytes/sec), the top speed of the tape (6.4 MBytes/sec), and what I know of the size of the buffers in the tape drive (in this case, 8 MBytes - about 1.2 seconds worth of data), I have my doubts about this.


In other words, I find it hard to believe that an 800 Mhz PowerPC can't drive 6.4 MB/s (max speed of the drive). That's pretty unimpressive.


Maybe Retrospect 6, processing, and lord knows what is burning all the cycles, but it's still unimpressive if true.


I *have* noticed that when writing a tape on retro 6.1, the CPU is very busy, which I would not expect if all it was doing is pushing data to the tape drive. For that matter, the CPU is pretty busy when writing tape with Retro 9, too. Even if you assume that the checksums and MD5 hash calculations are burning some of the cycles, it's hard to see that being hard to do at 6.4 MBytes/second.


In any case, it's much better with Retro 9.

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Another thing that comes to mind is file size. It's much faster reading/backing up a few dozen files than millions of files, even if they add up to the same number of GB. That's especially true of an 800MHz PowerPC, which would be over 10 years old by now. Hard drive speed has increased since then. :)

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