Shrinking ova file

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The Problem

I wanted to export a virtual machine and send it to a customer. However when I exported the OVA file, it was a massive 12GB. I have exported this virtual machine before and normally the ova is 2GB.

First, I check to see if some log file has ballooned in size or some other similar issue. However du -h -d 0 / and df -h seemed to agree the used disk space was only 6.2GB.

The Solution

Searching for causes of large ova files. I found a super user question that suggested that vmdk files (contained in ova files) write the whole sector for every sector that has a single non-zero bit. Searching for ways to compress vmdk files I found a page with this solution:

cat /dev/zero >zero.fill; sleep 1; sync; sleep 1; /bin/rm -f zero.fill

This line will completely fill the disk with zeros, and then raise an error once the disk is full. Next, it sleeps for a second and then flushes the file system buffers. Lastly, after sleeping for another second, it removes the zero filled file.

The Result

After running the command above on the guest operating system. I exported the machine to a new ova. This time the ova file was only 1.5 GB. Much better!