Zeroing out disk fills RAM of host (linux only)

alans · Post by **alans** » 20. Feb 2016, 01:07

Using virtualbox 5.0.14 I am currently zero filling a vm in order to compact the artifact's disk size. It looks like this:

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dd if=/dev/zero of=/EMPTY bs=1M
rm -f /EMPTY

This works great on my mac. Doing the exact same thing on a linux host causes the RAM to fill up on the host machine and the box getting OOM killed. The guest machine seems to be writing directly to the host's memory. There is a 1:1 ratio for zeros written in GB to GB of ram taken up.

So far I have tried to use sync to write data out to disk:

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i=0
while [ $? -eq 0 ]; do
  i=$(($i + 1))
  echo "writing EMPTY-$i..."
  sudo dd if=/dev/zero of=/EMPTY-$i bs=1M count=1000
  sync
done

I have also tried to turn hostiocache off:

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VBoxManage storagectl <vmname> --name "IDE Controller" --hostiocache off

What am I missing here? Is there anything else I can tweak so I am not caching disk writes on the host's memory?