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Date: Thu, 22 Dec 2005 19:28:26 -0500
From: Parv <parv@pair.com>
To: Tim Lastine <tim.lastine@hi.umn.edu>
Message-ID: <20051223002826.GA40026@holestein.holy.cow>
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	freebsd-questions@freebsd.org
References: <7.0.0.16.0.20051222100521.01ed28d8@smig.net>
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Cc: freebsd-questions@freebsd.org
Subject: Re: Inconsistencies in df
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in message <7.0.0.16.0.20051222100521.01ed28d8@smig.net>,
wrote Tim Lastine thusly...
>
> We are wondering why df gives such peculiar outputs on large disk 
> drives?  The used space and the available space do not add up the 
> reported size of the partition.  Is this a problem, or is it just the 
> way it is?  We are using a 250 Gig SATA (ad4) drive and a 1000 Gig 
> SATA Raid 0(da0) drive
...
> canicula-a# df -h
> Filesystem   Size   Used   Avail  Capacity  Mounted on
> /dev/ad4s1a  2.9G   55M    2.6G   2%        /
...
> canicula-a# df
> Filesystem  1K-blocks    Used      Avail   Capacity Mounted on
> /dev/ad4s1a   3049102   56150     2749024     2%    /
...
> /dev/ad4s1f  64489864       4    59330672     0%    /opt
> /dev/da0s1d 949613700       4   873644600     0%    /raid
> /dev/ad4s1e   4058062   29730     2903688    22%    /usr
> /dev/ad4s1d   3045006     302     2801104     0%    /var

(Tabs were evil in the above case as df outputs were not lined up
correctly; i have readjusted the above.)

Try to take 8% reserve in account ...

  df -t ufs \
  | tail +2 \
  | awk ' { sum = $3 + $4 +  $2 * 0.08 ;
            printf "%s: space diff: %f\n" , $1 , $2 - sum
          }
        '

... subject to rounding errors.  Here is an example ...

  # df
  Filesystem  1K-blocks     Used   Avail Capacity  Mounted on
  /dev/ad0s2a    138606    51952   75566    41%    /
  devfs               1        1       0   100%    /dev
  /dev/ad0s2d    594926   417042  130290    76%    /usr
  /dev/ad0s2e    475886    95826  341990    22%    /var
  /dev/ad0s2g  16724102 11949534 3436640    78%    /misc
  /dev/ad0s2f   2875822    16170 2629588     1%    /work
  procfs              4        4       0   100%    /proc

  # df -t ufs | tail +2 | awk '{ ... }' # awk program is given above
  /dev/ad0s2a: space diff: -0.480000
  /dev/ad0s2d: space diff: -0.080000
  /dev/ad0s2e: space diff: -0.880000
  /dev/ad0s2g: space diff: -0.160000
  /dev/ad0s2f: space diff: -1.760000


  - Parv

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