ZFS - cannot remove No space left on device

[nry]

Bit of misjudgement made in my process of moving to ZFS. My RAID6 array was smaller than my intended new ZFS pool and due to a difference in block sizes I ended up filling 100% of the space on my ZFS pool.

root@nas: df -h
z2-7200                17T   17T     0 100% /media/z2-7200

Oops! Bit of searching shows I'm not the first to make this mistake, and that you should be able to empty the contents of a file doing:

echo > /media/z2-7200/ISOs/Ubuntu.iso
bash: /media/z2-7200/ISOs/Ubuntu.iso: No space left on device

Also tried

dd if=/dev/null of=/media/z2-7200/ISOs/Ubuntu.iso
dd: /media/z2-7200/ISOs/Ubuntu.iso: No space left on device

Now this seems to have solved it for everyone else, what am I doing wrong?

Any suggestions on how this can be fixed?

 

[nry]

Fixed it, had to run this command on about 30 odd files (all 200-500mb) before it actually cleared some space!

 

[idownes]

I've never had to use it but the solution I've read is to truncate a file to zero length, e.g.,

truncate -s 0 filename

 

[gea]

My preferred solution is to add a small reservation to the pool itself. On problems, you can remove that.
With napp-it I add a default 10% reservation when you create a pool. This avoids also a massive performance degration
on a pool nearly full situation.