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I expanded my mdadm RAID 5 from 5 to 6 4TB disks and grew the raid. That all worked well. After I tried to expand the ext4 filesystem in GParted, which failed because of the 16TB limit. Afther the failed try GParted showed the partition as 20TB and 19.6TB used, so shrinking the partition with gparted did not work anymore. When the partition was mounted the size was correctly displayed as 16TB, all the data was still there and accesible.

I unmounted the partition and checked it with e2fsck -fy (no errors), shrunk it with resize2fs -M which was successful and shrunk the partition to 14TB. I rechecked the partition again with e2fsck -fy (no errors) and mounmted the partition again and all the data was still there and the partition size was now 14TB and 100% full...

I unmounted the partition again and started GParted. GParted still displayed the partition as 20TB and 19.6TB used.

What went wrong and how can I fix it?

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  • Note: Partition size != filesystem size. Your ext4 partition is 14TB in size, but the partition is some larger size (20TB?) with a bunch of free space between the end of the filesystem and the end of the partition. May 28, 2015 at 18:50
  • Also, I would not run 6-disk RAID5 with ext4 (or any non-checksumming filesystem) with data that you cannot replace or regenerate from another source. My experiences with that was data corruption, silent data corruption everywhere. I generally recommend ZFS for large filesystems. May 28, 2015 at 18:53
  • @Darth Android Ahhhh... I feel so stupid right now... Of course... thats what happens when you use GUI tools for years without a problem, once you run in a problem you forget a step... I fixed it now with gdisk (deleted and recreated the partition)... Thanks for your pointer! Regarding the bit rot problematic, the server is mainly used as a mediaserver, the important data like family photos are backed up on a server running zfs (raidz) on 4 2TB disks...
    – Simon
    May 29, 2015 at 7:57

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