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Clean installation od Debian squeeze 6.0.6 x64 on intel atom 230, with 3 HDDs, with 3x500GB.

df -h shows :

datastore              size used  free   %   mounted
/dev/md0              917G  909M  870G   1% /
tmpfs                1001M     0 1001M   0% /lib/init/rw
udev                  996M  188K  996M   1% /dev
tmpfs                1001M     0 1001M   0% /dev/shm

df -i shows :

datastore              size used  free   %   mounted
/dev/md0             61054976   27582 61027394    1% /
tmpfs                 256087       7  256080    1% /lib/init/rw
udev                  254831     692  254139    1% /dev
tmpfs                 256087       1  256086    1% /dev/shm

It is ext3.

Please tell me, where did my 47 gigabytes go? It is a clean installation as you can see.

du -sh shows: 709M

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up vote 11 down vote accepted

Does this help?

man mkfs.ext3
-m reserved-blocks-percentage
   Specify the percentage of the filesystem blocks reserved for the
   super-user.   This  avoids  fragmentation, and allows root-owned
   daemons, such as syslogd(8), to continue to  function  correctly
   after non-privileged processes are prevented from writing to the
   filesystem.  The default percentage is 5%.
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So you say, everything is OK? Well, 5% is about 45 or 47Gigabytes. Is it possible to change from 5 to 3%? – MIrra Jan 15 '13 at 20:10
All works as defined, yes. :) To reduce the reserved blocks: tune2fs -m reserved-blocks-percentage /dev/md0 – tink Jan 15 '13 at 20:27

47G from 917G is close to 5%. This is the default amount of reserved blocks used for super-user aims. You can see that executing tune2fs -l /dev/md0 | grep "Reserved block count". -m parameter of tune2fs and mke2fs can change the default behavior.

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Don't dare touch that! That is breathing space, if the filesystem ever gets too full it will slow down to a crawl. Besides, root has a special dispensation and can use (some) oe the reserved space. – vonbrand Jan 21 '13 at 20:27

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