We were missing a line in cloudinit to install lvm, which is needed to merge disks.

Because of the instance type requested, it only has two ephemeral volumes maximum, even though we request four ephemerals.
Different types have different limits, so this isn't a code issue at all.
I assume this is fine, but if not we'll have to look at the instance types we're requesting for different workloads.

I'm going to propagate these changes to ngxbio[2-4] now. Mail to follow.

Best,

-Stephen