Linux shows much less disk space then summary of all disks

centosdisk-space-utilizationlinux

I have a CentOS server with 4 disks, each with 1TB that totals to 3.636 TB of usable space (according to http://www.jonathanlaliberte.com/2007/12/18/calculating-actual-hard-disk-space/).

But the server df command shows the following status:

Filesystem            Size  Used Avail Use% Mounted on
/dev/md1              5.5G  3.0G  2.3G  57% /
/dev/md3              2.7T  2.7T   55G  99% /media
/dev/md0              181M   12M  160M   7% /boot

The swap is:

Swap:         5721         12       5708

So on overall, I'm about 900 GB short.

Any idea where that space went, and how I can get it back?

Thanks!

Best Answer

How are the MD devices configured? If you use a RAID1 (mirroring) or Raid5 (striped with parity), you will loose capacity. A RAID1 will have half the capacity of all disks, and a RAID5 will have the capacity of n-1 disks.

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