Date: Wed, 16 Mar 2005 11:52:19 +0000 From: Alex Zbyslaw <xfb52@dial.pipex.com> To: Ludo Koren <lk@tempest.sk> Cc: freebsd-questions@freebsd.org Subject: Re: Backup on DDS-4 tapes Message-ID: <42381DF3.5060906@dial.pipex.com> In-Reply-To: <200503160953.j2G9rjKR003358@lk.tempest.sk> References: <200503140938.j2E9c2EM024428@lk.tempest.sk> <42370004.5060506@dial.pipex.com> <200503160953.j2G9rjKR003358@lk.tempest.sk>
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Ludo Koren wrote: >It doesn't help either... The result is the same. > > Just to check I'm understanding your problem correctly -- you're expecting to write much more data to the tape than is actually being written. If that's correct, then there's a couple things I can think of: 1) Your tape drive isn't doing hardware compression. Check the manual and see if there are any dip switches you need to set. (Make a note of how they're set before you change anything, so you can go back to what you had originally!). When you say the result is the same, if it used exactly the same number of tapes (down to the decimal point) then that definitely suggests that your tape drive is not compressing. 2) The data you're writing to the tape is already mostly compressed, so you won't fit as much as you might if it were uncompressed data. Also, the 40Gb per tape that you quote is, I think, the MAXIMUM amount of data the tape will take. It's only 20Gb native. 40Gb is how much will fit at optimum compression, which you never get. It's unlikely to be a FreeBSD problem because I regularly fit 6-7Gb on a DDS-2, which has a native size of 4Gb. I use dump options like the ones in my last message. --Alex
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