Providing temporary storage space to a VM: qcow, nfs etc

[Mayuresh <mayuresh%acm.org@localhost>]

I am using a Linux guest as a pkgsrc build server and the host isn't
particularly rich in disk space. So can't completely reserve all the space
required, but spikes in usage during compilation are accommodatable.

I was using qcow2 disk image, but as someone already pointed out it fills
up rapidly and I searched further on that - it doesn't actually delete
anything. I don't find an easy way to compress it other than using a qemu
tool to create a duplicate image and delete the old one.

Looking for something more conservative on space. So turned to network
file systems with the host. But they aren't particularly speedy. Here are
speeds shown by dd for write operations:

qcow2: 64MB/s - good but disk fills up rapidly, no easy way to shrink
nfs: 9.8MB/s - about 6 to 7 times slower than virtual qcow2 disk
sshfs: 1.8MB/s - no need as nfs does better

If I could reduce the gap between nfs and qcow2 even to some extent I'd
probably settle for that, as it gives me a lot of flexibility in storage.

Mayuresh