Backup on DDS-4 tapes

[Ludo Koren]

     > 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.

That's right. I suppose that 54GB of data could fit on 2 40GB tapes...

     > 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!).

I'll check this

     > 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.

I will do statistics about files.

     > 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

Thank, for your suggestions.

lk